Introduction

In recent years, a critical emerging issue for ecosystems has been the increasing global pressure of chemical or micropollutant stressors (Reid et al. 2019; Schuijt et al. 2021; Xiao et al. 2023). The emergence of new pollutants in water sources is causing worldwide concern due to its potentially harmful environmental impact (Basheer 2018b; Basheer and Ali 2018). Environmental contaminants induced by anthropogenic sources have been highlighted to possess adverse effects that lead to ecological imbalance and environmental degradation (Basheer 2018a; Nguyen et al. 2022a). Emerging pollutants in aquatic ecosystems have received significant concern due to the various adverse influences on health issues and the natural environment. For example, petrochemicals, pharmaceuticals and personal care products, pesticides (organochlorine compounds), and heavy metals, e.g., arsenic (As), mercury (Hg), lead (Pb), and cadmium (Cd), have infiltrated aquatic ecosystems, causing habitat losses and vital species damage, even when released at low concentrations (Tsygankov 2019; Vardhan et al. 2019; Kreutzer et al. 2022). The occurrence of micropollutants in environmental matrices is of major attention for various reasons, such as their ecotoxicity to aquatic organisms. For this reason, to evaluate the potentially harmful effects of chemical mixtures on aquatic ecosystems, it is necessary to enhance stress monitoring and identify any adverse ecological impacts (Brack et al. 2019; Xin et al. 2021; Nguyen et al. 2023b).

Chemical stressors or environmental stress can directly impact population development and growth rates by reducing the birth rate and/or enhancing their mortality. Cai et al. (2020) investigated the algal toxicity S. obliquus caused by textile and dye wastewater streams. Prolonged exposure time could lead to adverse effects on algae, potentially causing their death (Cai et al. 2020; Othman et al. 2023). It was also found that tiny-sized polymers, e.g., microplastics, inhibited algae, and the interaction between algae and microplastics, might affect their photosynthesis and growth (Sjollema et al. 2016). Several chemicals released into the environmental matrices are genotoxic for aquatic life. Consequently, chemicals could indirectly and/or directly damage deoxyribonucleic acid structure (Schuijt et al. 2021). Exposure to these chemicals could cause compromised immune function in organisms. Thus, for organic and inorganic xenobiotics, microalgae contribute a critical role in the dispersal, chemical fate, transport, and bioaccumulation of toxic chemicals. Further, due to the low treatment performance in wastewater treatment plants, several micropollutants are discharged into water columns with high levels, then can accumulate and lead to high ecotoxicity to many aquatic organisms (Pessôa et al. 2021, Nguyen et al. 2022a, Tuan Tran et al. 2022a, b). Though the contents of pharmaceutical and personal care products are relatively low (ppm or ppb) in a natural environment, they have high durability and bioactivity that can have negative impacts (Arpin-Pont et al. 2016). Significantly, drug and pharmaceutical residues in water must be considered to predict the toxicities (Ali et al. 2009; Ky et al. 2023). Recent investigations have investigated the ecotoxicology of various pharmaceutical compounds in microalgae (Chia et al. 2021). More and more consideration has been attended to pesticides (e.g., organophosphorus compounds), which adversely affect aquatic organisms and threaten human health through the food chains (Xu et al. 2022). Also, many issues concerning the bioavailability of engineered micro/nanoparticles, their uptake by algae/microalgae, and the ecotoxicity mechanisms still need to be investigated. On this basis, the perspectives for ecotoxicity investigations about the contaminants in algal responses must be discussed. Thus far, numerous articles have explored micropollutant abundance and impacts; however, regarding their interaction and ecotoxicology associated with multi-contaminants in the aquatic environment, research explicitly focusing on the challenges remains limited (Azizullah et al. 2022; Banyoi et al. 2022; Othman et al. 2023; Xiao et al. 2023). This work remarks a state-of-the-art review of the current trend on the ecotoxicity of micropollutants to algae. The present investigation aimed to examine the adverse impacts of various micropollutants, e.g., petrochemicals, bisphenol A, pharmaceuticals (antibiotics and drugs), per- and polyfluoroalkyl substances, pesticides, heavy metals, and synthetic nano/microparticles on algae. Thus, ecotoxicology response of algae to contaminants in aquatic environments can establish a significant foundation for aquatic toxicological and risk assessments.

Environmental stress

Anthropogenic-induced disturbances lead to biodiversity degradation in water bodies among the most threatened and vulnerable ecosystems. Pollutants are a significant contributor to producing reactive oxygen species. Changes in cover and land-uses are strong drivers of global environmental degradation, and these human stressors can influence benthic algae (Fierro et al. 2019). Harmful algal blooms greatly damage marine ecosystem risk and human health (Griffith and Gobler 2020; Balaji-Prasath et al. 2022). The adverse impacts of agriculture on the aquatic biota and environment have been elucidated (Gerth et al. 2017). Increased expansion of marine pollution by high cadmium (Cd) contents has highly affected the growth and development of brown macroalga, namely H. fusiforme (Zhu et al. 2011). Adverse influences of nanoparticles on aquatic living organisms and the environment have also been given much special consideration (Farré et al. 2009). Nanoparticles could have a high threat and reach high levels, posing a significant risk to aquatic ecosystems. The increasing industrial use of nanomaterials poses potentially harmful threats to ecosystems, mainly living organisms in the environmental matrices. For example, Suman et al. (2015) illustrated that cytotoxic zinc oxide nanoparticles cause microalgae C. vulgaris and induce severe oxidative stress. Observations of Kumaresan et al. (2017) demonstrated that sulfate stress impacted the pigment level in blue-green algae Spirulina (A. platensis) with decreased their growth. It indicated that A. platensis could alter the gene expressions specifically included in sulfur-dependent pathways and sulfur metabolism.

While occurring contaminants are released into the environmental matrices, novel ones are being emitted continuously, e.g., engineered nanomaterials, pesticides, aromatic pollutants, pharmaceutical and personal care products, metals, and so on. The emerging concern of micropollutants discharged by municipal and domestic wastewater treatment plants can have an ecological effect on aquatic living organisms and surrounding environments. Consequently, water contamination and degradation have become unexpectedly complex (Lu et al. 2021). Environmental stress—sources, fate, and adverse effects on the aquatic ecosystem, is shown in Fig. 1. These persistent harmful compounds and their metabolites may raise ecotoxicological threats and risks. For instance, emerging micropollutants are illustrated in complex mixtures with various physicochemical characteristics, resulting in adverse health impacts (Archer et al. 2017; Nguyen et al. 2022a). Concerning the threats to health issues, one of the major examinations related to pharmaceutical and personal care products exposure via the aquatic pathway is that it can interfere with and alter the endocrine system. The triazophos residues, a chemical compound used in insecticides, could enter aquatic ecosystems by direct overspray on agricultural fields, surface runoff, and air deposition by rain (Xu et al. 2022). Therefore, these residues cause huge attention and concern for potential health threats to natural ecosystems and humans. Pesticides could inhibit the growth rate, photosynthetic damage, and oxidative stress on algal cells (Xu et al. 2022). The accumulation, distribution, and transfer of emerging micropollutants, e.g., nano/microplastics and persistent organic pollutants in the food chains and webs, is a critical benchmark for investigating its ecological risks (Zheng et al. 2016; Nguyen et al. 2023a, 2023b). The essential ecotoxicological mechanisms of pollutants to aquatic organisms, such as algae, have identified reactive oxygen species generation, cell activity reduction, cell structure damage, and deoxyribonucleic acid damage (Chen et al. 2019). Micropollutants discharged into aquatic ecosystems can trigger biochemical and physiological characteristics and algal ecological responses.

Fig. 1
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Environmental stress sources, fate, and effects on the aquatic ecosystem. The environmental stress includes their origins, ecosystem pathways, and detrimental impacts on aquatic environments. The presence of hazardous substances and their by-products can increase ecological threats and risks significantly. WWTPs: wastewater treatment plants

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In the global scope, more than 770 pharmaceutical active compounds and their transformative products have been recognized (Couto et al. 2022). The properties of pharmaceutical and personal care products and their risks to the environmental ecosystems and human health issues are determined. The uncontrolled release of polycyclic aromatic hydrocarbons into aquatic ecosystems has posed high risks to aquatic organisms. Polycyclic aromatic hydrocarbons are known as toxic, mutagenic effects, and carcinogenic, particularly by generating reactive oxygen species, including singlet oxygen, hydrogen peroxide, and others. For this reason, their occurrence is considered aquatic micropollutants as a severe concern. Risk assessment induced various hydrocarbons such as polycyclic aromatic hydrocarbons in marine waters can usefully predict the toxicity and their effects on the aquatic ecosystem (Softcheck 2021). Polycyclic aromatic hydrocarbons can inhibit the growth, biochemical, and physiological compositions of the various algal species (Asghari et al. 2020; Tomar and Jajoo 2021). The chemical structure of algal species depends on environmental factors; that is, they can alter to adapt under abiotic stress conditions (Tomar et al. 2022). For example, unfavorable environmental conditions, including pH, temperature, salinity, and nutrient variations, might cause changes in the levels of lipids, carbohydrates, and pigments for microalgae growth.

With increasing awareness of the ecological threats of micropollutants, many efforts have been examined in the past years. Environmental quality degradation and ecological risk have become critical global concerns (Tuan Tran et al. 2022a, b; Nguyen et al. 2023b). Sources of contamination, e.g., the discharge of industrial and domestic streams under uncontrol or improper management, runoff from agricultural and urban areas, and less effective treatment technology, cause an increase in various pollutants into water bodies and aquatic ecosystems (Couto et al. 2022; Nguyen et al. 2022b; Tran et al. 2022a). The biological uptake of persistent organic pollutants through marine phytoplankton has significantly influenced persistent organic pollutants levels in water bodies. The fate, behavior, and transportation of persistent organic pollutants in the marine ecosystem could be affected by algae bioaccumulation and adsorption. The persistent organic pollutants uptake and their accumulation process are involved in a complex manner by cell density and exposure time, as well as critical environmental parameters, i.e., pH, nutrient levels, contents of colloidal and dissolved organic matter, and phytoplankton characteristics (Rhee and Thompson 1992; Qiu et al. 2017).

Further, the biodiversity of ecosystems may be impacted by environmental pollution, which is caused by human activities and even invasive species, which can pose a high risk (Quetglas-Llabrés et al. 2020). For instance, the invasive red algae L. lallemandii induces oxidative stress and affects coastal marine ecosystems, e.g., sea urchin P. lividus (Quetglas-Llabrés et al. 2020). Another critical property that might harm aquatic ecosystems is contamination from human activities. After algae adsorb pollutants such as polycyclic aromatic hydrocarbons, pharmaceutical and personal care products, and heavy metals, they are ingested by higher trophic levels, such as fish and shrimp, which are enriched along the food chains. Thousands of toxic micropollutants have been discharged into the marine environment that can adversely impact their biological functions. Aquatic ecosystems can also be influenced differently, associated with the type of pollution, location, and chronic or acute exposure. Particularly, polycyclic aromatic hydrocarbons are recognized as priority micropollutants, e.g., some polycyclic aromatic hydrocarbons have been indicated as an essential concern for the environment and health risk in the European Union and the USA (Samanta et al. 2002; Othman et al. 2023). Therefore, the potential effects of ecological threats regarding various micropollutants on algae have drawn increasing interest. It required that aquatic ecotoxicology combines toxicology and ecology to integrate and examine the impacts of contaminants via biological levels, from the molecular to cellular levels, aquatic communities and even ecosystems (De Boeck et al. 2022).

Ecotoxicology response of algae to contaminants

Chemical, biological, and physical factors influence the ecotoxicity of chemicals to algae, leading to effects at the biological community level that can become complex (Genter 1996; Elersek et al. 2021; Ford et al. 2021). Organic and inorganic chemical stress impacts algae at biological organizations' biochemical, cellular, community, and population levels (Li et al. 2022; Pastorino et al. 2022; Zhang et al. 2023). Micropollutants can accumulate in algae, leading to physiological and biochemical adverse effects due to their exposure are shown in Fig. 2. The significance of transition heavy metals, e.g., chromium (Cr), copper (Cu), arsenic (As), and mercury (Hg), and pesticides, namely herbicides, insecticides, and fungicides along with oil products in the induction of oxidative stress in an aquatic ecosystem is also highlighted (Lushchak 2011; Xiao et al. 2023).

Fig. 2
figure 2

Physiological and biochemical adverse effects of pollutant exposure on algae (ROS: reactive oxygen species, DNA: deoxyribonucleic acid, RNA: ribonucleic acid). Algae are susceptible to organic and inorganic chemical stressors, affecting them at various biological levels, including biochemical, cellular, community, and population. Micropollutants have the potential to accumulate within algae, resulting in adverse physiological and biochemical effects due to their prolonged exposure

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Polycyclic aromatic hydrocarbons

Global and local stressors highly threaten oil pollutants. Particularly, due to the incomplete combustion of living and fossil fuel types, petroleum processing or oil spills, industrial and urban runoff, and so on from human activities and natural sources that polycyclic aromatic hydrocarbons can enter aquatic ecosystems (Boehm and Page 2007; Nizzetto et al. 2008; Zhang et al. 2021). Uptake and polycyclic aromatic hydrocarbons accumulation in food chains and ecosystems have been recognized as significant health and environmental concerns. Figure 3 presents an illustration of microalgae response to polycyclic aromatic hydrocarbons exposure.

Fig. 3
figure 3

Microalgae response to polycyclic aromatic hydrocarbons exposure (PAHs: polycyclic aromatic hydrocarbons). Exposure to polycyclic aromatic hydrocarbons induces significant stress responses in microalgae, leading to changes in enzymatic activities and biochemical compositions. Polycyclic aromatic hydrocarbons have the potential to modify cell membrane permeability by influencing lipids and proteins, indicating a negative impact on algal cells and their normal functioning. These effects depend on environmental factors such as pH, temperature, salinity, and ultraviolet radiation

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Several studies concluded that polycyclic aromatic hydrocarbons in the water column could cause an indirect impairment of aquatic environmental ecosystem health by these contaminations. More severe stress responses by polycyclic aromatic hydrocarbons-exposed microalgae could change enzymatic activities and biochemical contents (Othman et al. 2023). Due to the hydrophobic properties of polycyclic aromatic hydrocarbons, algal lipid level is influenced by this exposure and could cause damage to the cells. Depending on exposure doses, polycyclic aromatic hydrocarbon exposure to microalgae (e.g., single compounds and/or mixture) could lead to a decline in growth rates, photosynthetic, and biomass (Othman et al. 2023). These micropollutants can alter the functional absorption of photosystem II and the fluorescence yield, both critical proxies for the photosynthetic process. Furthermore, environmental conditions or factors, e.g., temperature and sunlight radiation, can also increase the algal community's ecotoxicity of polycyclic aromatic hydrocarbons.

Polycyclic aromatic hydrocarbons are toxic to organisms because they can interfere with the membrane functions of enzymes or proteins in cellular membranes. Regarding polycyclic aromatic hydrocarbons toxicity to microalgae, S. capricornutum (green microalgae) cultivated with anthracene illustrated a growth inhibition with a half-maximal inhibitory concentration of 16 µg L−1, and the anthracene toxicity contributed to increasing the ultraviolet A light exposure of the alga (Gala and Giesy 1994). The microalgae T. chuii exposed to phenanthrene, anthracene, and naphthalene for 96 h reported a growth restraint that the ecotoxicity was, respectively, phenanthrene—anthracene—naphthalene, and this ecotoxicity was promoted by the increase of temperature (Vieira and Guilhermino 2012). Also, Kottuparambil and Park (2019) showed that the microalgae E. agilis cultivated with rising anthracene levels varied from 0.35 to 84 µM for 96 h, indicating a reduced in the content of carotenoids and chlorophylls, in photosynthetic efficiency, and in growth. The Ulva lactuca (known as green macroalga) exposed to gasoline involving naphthenic, paraffinic, aromatic, olefinic hydrocarbons, and isoparaffinic demonstrated a reduction in carotenoids, chlorophylls, and polyphenols contents (Pilatti et al. 2016). Anthracene caused a significant increase in lipoperoxides due to oxidative degradation reaching a 24-h maximal level, showing that oxidative stress caused Chlorophyta’s membrane damage (González et al. 2021). The potentially toxic M. aeruginosa responded to anthracene contamination by altering the microcystin biosynthesis gene clusters (Bi et al. 2016). A substantial increase in microcystin level was demonstrated after 12-day exposure; consequently, the gene mcyB was repressed, indicating that polycyclic aromatic hydrocarbons pollution in the aquatic ecological community can cause unexpected alternations and harmful changes.

Polycyclic aromatic hydrocarbons are a group of organic chemical compounds comprising two or more joined-together aromatic rings categorized as persistent organic contaminants. Recently, the polycyclic aromatic hydrocarbon effects on microalgae have been carried out by Othman et al. (2023). Photosynthesis, the critical process conducted by algae, takes place to be the most influenced by polycyclic aromatic hydrocarbons exposure. Due to its hydrophobic nature, polycyclic aromatic hydrocarbons-related ecotoxicity effects on algae can interfere with cell biomolecules. Polycyclic aromatic hydrocarbons can cause severe stressors such as oxidative stress or membrane damage to algae. The influences of polycyclic aromatic hydrocarbons are determined by both species- and dose-dependent and are affected by environmental conditions, e.g., temperature, salinity, ultraviolet radiation, etc. (Othman et al. 2023). Further, Tomar et al. (2022) investigated the bioremediation of Chlorella vulgaris for several polycyclic aromatic hydrocarbons (such as naphthalene, anthracene, and pyrene) and their effects on the growth and photosynthesis of C. vulgaris. Under seven-day polycyclic aromatic hydrocarbons exposure, the growth of algae C. vulgaris was impacted within the order of pyrene—anthracene—naphthalene. Concerning biomolecules, polycyclic aromatic hydrocarbons experiments reported a notable reduction in lipid levels, especially the ecotoxic impact of pyrene was also marked. Polycyclic aromatic hydrocarbons might alter the permeability of cell membranes by influencing their lipids and proteins. This indicates that polycyclic aromatic hydrocarbons negatively affect the algal cells and can change their functioning.

Bisphenol A

In those days, high concentrations of serious toxicants were found in the ecosystems causing chronic and acute influences (Schmitt-Jansen et al. 2008). Prominent illustrations come from significant exposures to endocrine-disrupting chemicals such as bisphenol A. These ecotoxicants are usually characterized by long persistence, high toxicity, and bioaccumulation. For a comprehensive investigation, the molecular responses of algae related to bisphenol A exposure have been presented (Azizullah et al. 2022). Due to their extensive applications in industrial products, e.g., epoxy resins (polyepoxides) or polycarbonate plastics, bisphenol A is an emerging micropollutant, causing an increase in environmental pollution and detrimental influences on organisms. Bisphenol A negatively disturbs algae species by inhibiting various biochemical and physiological processes (Azizullah et al. 2022). They could induce cytotoxicity, neurotoxicity, genotoxicity, reproductive toxicity, and endocrine system disruption in exposed aquatic life (Bonefeld-Jørgensen et al. 2007; Yang and Hong 2012; Guo et al. 2017). For instance, after ten-day exposure, bisphenol A at 50 mg L−1 induced serious growth restraint of 18% in C. mexicana and 85% in C. vulgaris (Ji et al. 2014).

The half maximal effective concentration (EC50) obtained 9.9 mg L−1 in P. subcapitata after 72-h exposure indicated that bisphenol A can inhibit the growth of P. subcapitata (Elersek et al. 2021). Bisphenol A exerted comparable toxic potential EC50 was below 3.5 mg L−1 in D. subspicatus (Tišler et al. 2016). Further, higher EC50 values were reported, varying from 20 to 89 mg L−1 for algae species such as C. mexicana and C. vulgaris (Ji et al. 2014). Findings also indicate that algal species are more sensitive to bisphenol A. Czarny-Krzymińska et al. (2022) examined microalgae in 14-day exposure time to bisphenol A that indicated EC50 varied from 42.1 to 42.5 mg L−1 and toxically adverse impacts to their structural congeners.

Due to widespread distribution and occurrence in aquatic ecosystems, bisphenol A can pose threats to the producers, typically algae (Czarny-Krzymińska et al. 2022). Previous investigations have indicated that bisphenol A harms aquatic living organisms and could lead to endocrine-disrupting impacts, especially potentially related to a variety of other contaminants, causing adverse health consequences (Liang et al. 2021; Wang et al. 2021). The effects of bisphenol A on chlorophyll level, cell growth, and oxidative stress of algae C. pyrenoidosa have been reported (Li et al. 2022). Thus, evaluating bisphenol A's influences on algae species in aquatic ecosystems gives essential data aid to investigating their potential threats. The level of bisphenol A affected the chlorophyll synthesis, recommending that oxidative stress may inhibit cell growth. Further, the increased negative impact caused by a mixture of chemicals poses a significant threat to microalgae.

Pharmaceutical and personal care products

Pharmaceutical and personal care products involve thousands of various chemical compounds, e.g., nonsteroidal anti-inflammatory drugs and antibiotics, prescription and/or nonprescription drugs, illegal drugs, veterinary drugs and their metabolites, hygiene products, cosmetics, bath, and hair products (Cizmas et al. 2015). Anthropogenic activities cause exposure of a living organism, such as algae, to active endocrine substances and endocrine disruptors. The primary sources of pharmaceutical and personal care products are the pharmaceutical industry, aquafarms, agricultural areas, wastewater treatment plants, and effluents, especially untreated sewage from hospitals (Luo et al. 2018; Lu et al. 2019; Tran et al. 2022b). Pharmaceutical and personal care products can cause unexpected impacts on algae species and their communities (Xin et al. 2021). Therefore, multiple algae endpoints can be applied to illustrate an entire assessment of the ecotoxicity of pharmaceutical and personal care products. Miazek and Brozek-Pluska (2019) conducted a review concentrating pharmaceutical and personal care products' ecotoxicity on microalgal growth and metabolism. Several algal species showed sensitive responses to pharmaceutical and personal care products contamination, e.g., P. subcapitata, C. vulgaris, C. pyrenoidosa, S. obliquus (Wang et al. 2016). pharmaceutical and personal care products can affect algal biochemical and physiological properties (Lushchak 2011). Algal metabolism is likely related to the transport and biochemical processes involved by pharmaceutical and personal care products. Several common reactive oxygen species, i.e., superoxide, hydroxyl radical, and hydrogen peroxide induced by pharmaceutical and personal care products, which could induce biomolecular damage, including ribonucleic acid, deoxyribonucleic acid, lipids, and proteins (Martín-Díaz et al. 2009; Lushchak 2011). Moreover, the influences of pharmaceutical and personal care products on the algae community can be assessed by toxicity and their bioaccumulation. Due to similar physicochemical characteristics, pharmaceutical and personal care products could cause impacts on algal communities, e.g., those with an octanol–water partition coefficient ≥ 3 to be bioaccumulated potential to algae (Van der Oost et al. 2003). Cytarabine, also known as cytosine arabinoside, is likely to be inhibited the growth and development of algae with EC50 varying from 53 to 100 mg L−1 (Zounkova et al. 2010).

As they are a fundamental group of emerging organic contaminants, there is a rising concern related to the severe impacts of pharmaceutical contamination. Antibiotics and nonsteroidal anti-inflammatory drugs are a group of fundamental drugs characterized, e.g., able to be highly persistent in the environmental matrices, are widely prescribed globally, and lead to long-term ecotoxicity. It also was investigated to examine the ecotoxicity in various living organisms (Magdaleno et al. 2015; Minguez et al. 2016; Wang et al. 2020). Similarly, De Boeck et al. (2022) investigated the ecotoxicity of various antibiotics and nonsteroidal anti-inflammatory drugs on green algal species, including D. spinosus and Chlorella sp. Based on the 96-h median effect concentration values, findings demonstrated that tetracycline was usually more toxic than other antibiotics such as amoxicillin and ciprofloxacin; meanwhile, paracetamol is considered to be a higher risk compared to diclofenac and ketoprofen. Pharmaceutical compounds cause adverse effects on microalgae metabolism and growth through disruption of the photosynthetic and gene expression, as well as dramatically enhancing reactive oxygen species formation and altering the activities and functions of antioxidant enzymes (Chia et al. 2021).

Per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances are a kind of chemical compound used globally and approximately 4700 synthetic chemicals (Banyoi et al. 2022). They have been utilized in commercial and industrial products since the 1950s. These per- and polyfluoroalkyl substances are applied in various products and found in environmental matrices and living organisms around the world. From daily usage and manufacturing processes, and due to their high bioaccumulation and persistency in the environment, per- and polyfluoroalkyl substances distribute commonly in aquatic ecosystems, leading to potential ecotoxicity (Buck et al. 2011). Some per- and polyfluoroalkyl substances are a large family of persistent industrial chemical compounds with endocrine-disrupting characteristics that are harmful and considered as endocrine-disrupting chemicals. Per- and polyfluoroalkyl substances contamination can affect the algae and cause severe impacts on higher trophic organisms. Many investigations have illustrated the ecotoxicity of long-chain per- and polyfluoroalkyl substance on several aquatic life (e.g., fish, algae, or Daphnia, etc.), highlighting that algae are one of the most sensitive life forms to per- and polyfluoroalkyl substance-contaminated environments (Ding et al. 2012).

In the research of Niu et al. (2019), three concentrations (10 ng L−1 to 1000 ng L−1) for these per- and polyfluoroalkyl substances were tested to examine the toxical response of algae Chlorella sp. for an exposure time of 14 days. The emerging per- and polyfluoroalkyl substances could affect aquatic ecosystems, these influences extremely inhibit the growth of algae Chlorella sp. For instance, per- and polyfluoroalkyl substances are conveyed from the inland to pose a potential risk to marine, these pollutants may induce oxidative stress and affect physiological processes and algal growth (Mallick and Mohn 2000; Niu et al. 2019). Liu et al. (2008) indicated that perfluorooctanesulfonic acid impeded the growth and development of algae S. obliquus with a 96-h median effect concentration of 99.9 mg L−1. Per- and polyfluoroalkyl substances could enter the aquatic ecosystem from several sources, e.g., leakage from the production of fluorochemicals, atmospheric disposition, firefighting foams, industrial and household activities, and/or wastewater treatment plants (Evich et al. 2022).

Among per- and polyfluoroalkyl substances, perfluorooctane sulfonic acid and perfluorooctanoic acid were determined to be the two main kinds discharged to the environment. Per- and polyfluoroalkyl substance, particularly those with longer carbon chains, particularly perfluorooctanoic acid or perfluorooctane sulfonic acid, have been reported to be environmentally persistent, with ecotoxic impacts associated with bioaccumulation potential (DeWitt et al. 2012; Fenton et al. 2021). Emerging per- and polyfluoroalkyl substance mixture can interrupt photosynthesis, reactive oxygen species metabolism, and deoxyribonucleic acid replication in algae C. pyrenoidosa, demonstrating the environmental threats and risks (Liu et al. 2022). Although these per- and polyfluoroalkyl substance levels in the environmental matrices are relatively low (ng L−1–mg L−1), the exposure to per- and polyfluoroalkyl substances mixture caused exhibits more substantial toxic impacts than individual per- and polyfluoroalkyl substance on algae. Under the per- and polyfluoroalkyl substances mixture exposure, the gene expression linked to deoxyribonucleic acid replication was interrupted, inhibiting the algae growth. The wide use and persistent occurrence of emerging per- and polyfluoroalkyl substances in the aquatic ecosystem could cause toxical influences, particularly some per- and polyfluoroalkyl substance such as GenX chemicals, which could disorder the metabolism of algae C. pyrenoidosa (Li et al. 2021; Liu et al. 2021b).

Pesticides

In agricultural activities, widespread use of pesticides, e.g., organophosphorus compounds, leads to massive residues in environmental matrices, especially in aquatic ecosystems. Regarding pesticide accumulation, pesticide levels in the aquatic environment have increased over time. Pesticides can cause indirect and/or direct ecotoxicity to microalgae. For instance, Chlorella pyrenoidosa has been applied as an algal species in ecotoxicological investigations for risk examination of organophosphorus compounds (Chen et al. 2016). Du et al. (2023) illustrated that temperate and Arctic microalgae were sensitive to insecticides, e.g., such as trifluralin and chlorpyrifos, regarding pesticide ecotoxicity. Furthermore, the growth of temperate microalgae, e.g., M. bravo, C. neogracile, and Arctic microalgae, e.g., M. polaris, C. neogracilis, was acutely inhibited at the chlorpyrifos concentrations at 500 µg L−1 and 200 µg L−1 (Du et al. 2023).

Several herbicides adversely impact photosynthesis due to damaging cellular oxidative induced by reactive oxygen species accumulation and formation. It was illustrated that the oxidative stress and sensitivity caused by pesticides to algal species (Medithi et al. 2021). The 96-h acute toxic effects of triazophos (1.0 and 10 mg L−1) on the algae Chlorella pyrenoidosa were also reported (Xu et al. 2022). Findings indicate that the algal cellular structure was damaged by triazophos exposure, and the growth of algae C. pyrenoidosa was dramatically reduced by pesticides such as triazophos. More significantly, it was shown that the inhibition rates were decreased by 25.7% (1.0 mg L−1) and 39.5% (10 mg L−1) after 96-h exposure, respectively. Also, results showed that oxidative stress damage in C. pyrenoidosa and their growth was notably inhibited by triazophos with the 96 h-EC50 was 12.79 mg L−1. The growth inhibition of algae was accordant with the raised intracellular reactive oxygen species, malondialdehyde level, and activity of antioxidant enzymes illustrating lipid peroxidation and oxidative damage in the algal cells. Further, the toxic response of the freshwater algae S. obliquus has experimented with herbicides, e.g., fenhexamid, atrazine, and lactofen (Mofeed and Mosleh 2013; Cheng et al. 2015). Kurade et al. (2016) described that the green microalgae C. vulgaris responded to diazinon by enhancing the algal enzymatic antioxidant in 12-day exposure time. Therefore, ecotoxicology is essential to investigate an in-depth knowledge of their toxicity, the action mode of pesticides, and the adverse effects at the population and/or organism level.

Heavy metals

Heavy metals originated from wastewater treatment plants and industrial activities contaminating the environment, and they are long-standing due to their non-biodegradable properties, which are ecotoxic to ecosystem threat and human health (Phan et al. 2020; Zamani-Ahmadmahmoodi et al. 2020; Xiao et al. 2023). Heavy metals have been recognized as an adverse global environmental risk due to their wide occurrence, distribution, high bioaccumulation, and biotransformation. The occurrence, distribution, and fate of heavy metal contaminants in aquatic environments critically rely on the characteristics of industrial fields, e.g., mining, paint, metallurgy, battery, hair dye, machinery, electroplating process, and so on, and daily urban activities, e.g., traffic emissions, air deposition, and domestic waste streams (Hepburn et al. 2018; Saleem et al. 2019). Heavy metals can be accumulated in microalgae and then aggregate transfer at higher trophic organisms via the food chains and webs. Moreover, heavy metals can alter important cofactors in proteins and enzymes, leading to abnormal metabolism in algae (Lu et al. 2021). These peculiar processes produce excessive reactive oxygen species, an important cause that induces adverse impacts. Consequently, they can severely damage cellular components, i.e., proteins, lipids, nucleic acids, amino acids, and lipid membranes (Qian et al. 2011; Jamers et al. 2013; Byeon et al. 2021). More seriously, heavy metals severely impact the algal community and may lead to their death (Xiao et al. 2023). However, the harmful impacts are associated with heavy metal species, levels, and environmental factors. For instance, the growth of Chlorella vulgaris can be inhibited at 60 μmol L−1 Zn(II) and 80 μmol L−1 Cd(II) (Leong and Chang 2020). Growth inhibition is also associated with the microalgae species and the exposure time to metals. Concerning response to cadmium (Cd) exposure of brown algae S. fusiforme, Zhang et al. (2015) reported that an increase in Cd ion could lead to a significant reduce in algae growth rate. Cd-related ecotoxicity could disrupt and alter membrane integrity, and inactivate the enzymes of multiple metabolic processes, consequently the disturbances in response inhibition of algal physiological activities (Lee and Shin 2003; Zhang et al. 2015).

Microalgae respond to a toxic environment by altering intracellular ultrastructure and cell morphology, e.g., cellular size, cellular debris, cytoplasmic vacuolation, starch accumulation by granules, and electron-dense granules (Xiao et al. 2023). The critical responses of microalgae to heavy metal stress were previously examined, e.g., Scenedesmu, Chlorella, Chlamydomonas reinhardtii, Cyanobacterium, etc. (Pradhan et al. 2019; Gu et al. 2020; Geng et al. 2021). The ecotoxicological responses vary between microalgae species and heavy metals (Table 1). Major challenges in aquatic ecotoxicology are that communities are exposed to multiple stressors. It shows heavy metals cause significantly influence the physiological and biochemical processes of microalgae. Under heavy metal-induced stress, living organisms such as microalgae can generate several extracellular polymeric substances, i.e., proteins, lipids, polysaccharides, non-polymeric substances, uronic acids, etc. For detail, associated with the characters of the functional groups and cell surface, extracellular polymeric substances could be engaged in the sorption of heavy metal ions (Naveed et al. 2019). Moreover, high heavy metal levels strongly impact algae's biochemical and physiological processes, including cell ultrastructure, photosynthesis, growth, the composition of fatty acids, and protein content (Xiao et al. 2023). Heavy metals can cause the formation of critical reactive oxygen species (e.g., singlet oxygen, hydroxyl radicals, and hydrogen peroxide) in cells, which primarily induces the oxidation damage of lipid, protein, and thiol peptides, as well as activation of the antioxidant system (Fig. 4). Heavy metals exert a toxic influence on algae at molecular and cellular levels (Priyadarshini et al. 2019). The high contamination of heavy metals damages the cellular system, and further alters its populations. Interaction between algae and toxic heavy metals adversely impacted their physiological, biochemical, and enzymatic activities, ultimately causing their death.

Table 1 Ecotoxicological response of algae to contaminants in aquatic environments
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Fig. 4
figure 4

Toxic influence on algae induced by heavy metals (DNA: deoxyribonucleic acid, 1O2: singlet oxygen, H2O2: hydrogen peroxide, *OH: hydroxyl radicals). Heavy metals have the potential to generate harmful reactive oxygen species, such as singlet oxygen (1O2), hydroxyl radicals (*OH), and hydrogen peroxide (H2O2). This process primarily leads to oxidative damage in lipids, proteins, and thiol peptides. The levels of heavy metals significantly affect various biochemical and physiological processes in algae, including alterations in cell structure, photosynthesis, growth, fatty acid composition, and protein content

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Synthetic nano/microparticles

Over the last few years, an increase in reports on the unexpected effects of nano/microparticles on algae has been demonstrated (Middepogu et al. 2018; Pereira et al. 2020; Pastorino et al. 2022; Minh-Ky et al. 2023). Carbon-based nanomaterials, e.g., carbon nanotubes, graphene, and fullerenes, have been recognized in aquatic ecosystems. The literature search revealed that the presence of nanoparticles such as carbon nanotubes would enter natural aquatic environments in combination with other organic compounds. For instance, exposed to carbon nanotube of Pseudokirchneriella subcapitata with EC50 up to 17.95–20 mg L−1 regarding the toxicity sensitivities (Schwab et al. 2011; Lukhele et al. 2015). Kwok et al. (2010) conducted Thalassiosira pseudonana exposure to multi-walled carbon nanotubes, leading to growth and development inhibition of microalgae reaching EC50 of 1.9 mg L−1.

Among engineered nanoparticles, metal oxide nanoparticles are commonly used in various commercial products and are causing concerns about their potentially harmful influences on environmental health and human beings (Aschberger et al. 2011; Banu et al. 2021; Grasso et al. 2022). To observe the ecotoxicity mechanism, algae C. vulgaris were tested with 50, 100, 200, and 300 mg L−1 zinc oxide nanoparticles for exposure of 24 h and 72 h (Suman et al. 2015). The cytotoxicity assay measure indicated a substantial decrease in the viability that depended on the exposure time and dose. The cell wall damage and substantial morphological alternations were confirmed by Suman et al. (2015). Investigations of the zinc oxide nanoparticles biotoxicity illustrate critical mechanisms of nanoparticle influence, indicating their potentiality to release free Zn(II) ions, which could synergistically promote reactive oxygen species production, resulting in oxidative damage in cells. Overproduction of reactive oxygen species is reported to be the most important mechanism of nanoparticle toxicity (Sharifi et al. 2012; Pastorino et al. 2022). In this manner, chemical reactions occur, leading to increasing formation and accumulation of reactive oxygen species, such as superoxide radicals, causing oxidative stress.

Toxic influences on green alga A. superbus were investigated and supported on various associations of nano-zinc oxide, Degussa P25-titanium dioxide, and antimicrobial agents (i.e., triclosan) under multiple illuminations (Xin et al. 2020). Degussa P25 is primary for the antioxidant enzyme, lipid peroxidation, and oxidative stress. Degussa P25*nano-zinc oxide is the critical interaction of micropollutants, influencing lipid peroxidation, macromolecules, and photosynthesis. When nano-zinc oxide, Degussa P25, and triclosan enter into natural ecosystems simultaneously or individually, they could cause various impacts on aquatic algae. Similarly, various aquatic organisms also can exhibit sensitivity to nanomaterials. Trace levels at 10 µg L−1 of silver nanoparticles can activate the growth and development of algae in experiments (Lu et al. 2020). The ecotoxicity of silver nanoparticles was reported to result in interactions of the dissolution, particle uptake, and cause of oxidative stress for living organisms (Liu et al. 2021a). It showed the bio uptake, physiological responses, and metabolic perturbations related to interactions of citrate-coated silver nanoparticles (20 nm) with the alga P. malhamensis. The silver nanoparticle exposure increased with time and induced meaningful bioaccumulation of Ag into an algal cell. Also, other results showed high sensitivity to a broad range of toxic nanoparticles, such as n-titanium dioxide and n-zinc oxide to algae species C. tenuissimus (Pastorino et al. 2022).

Regarding the impacts of combined exposures of nano/microplastic particles and chemicals, these particles can facilitate the bioaccumulation of micropollutants into exposed organisms. Previous investigations demonstrated that tiny particle sizes of microplastics had higher ecotoxicity in the microalgal community (Chae and An 2017; Alimi et al. 2018; Natarajan et al. 2022). Microplastic items are well highlighted as directly great risks to freshwater organisms, e.g., microalgae, they also indirectly affect the aquatic ecosystem by adsorbing and acting as a significant pathway for the fate and transportation of toxic micropollutants. In addition, the combination of various microplastics (e.g., polyethylene, polystyrene, and polyvinyl chloride) and antibiotic drugs (e.g., triclosan) resulted in oxidative stress and antagonistic effect on growth inhibition on algae S. costatum (Zhu et al. 2019). Findings indicate that the distribution of organic micropollutants can affect the microplastic influences, and the ecotoxicity of microplastics on microalgae mainly causes physical damage. Thus, the interaction of microplastics and antibiotic drugs could potentiate toxic impacts on aquatic living organisms.

It is documented that the ecotoxicity regarding carbon-based nanomaterials to algae cells could be included in direct exposure and indirect effects, e.g., negative effects on photosynthesis, light absorption, and nutrient depletion (Long et al. 2012; Zhao et al. 2017). For example, Zhao et al. (2017) examined the ecotoxicity of graphene-based nanomaterials and showed a substantially reduced membrane integrity of freshwater algae cells C. pyrenoidosa. A similar observed result was exposed to carbon nanotube for Pseudokirchneriella subcapitata with EC50 of 17.95 mg L−1 (Lukhele et al. 2015). Micro- or nanoparticles, including carbon nanotubes and silver nanoparticles, promoted reactive oxygen species production, leading to oxidative stress in microalgae and inhibition of algal growth (Zhang et al. 2017).

For more details, nanoparticles often carry various functional groups, resulting in strong adsorption capacities to other toxic pollutants. The wide application of nanomaterials or their technology causes the emission of engineered nanoparticles discharged into aquatic ecosystems. Entrapping nanotitanium dioxide of algal cells plays an important role, leading to ecotoxicity to algae Pseudokirchneriella subcapitata (Aruoja et al. 2009). In particular, nanoparticles (1–100 nm) can transport pollutants and alter their mobility, toxicity, transformation, and bioavailability (Besha et al. 2020). Ecotoxicological research is a critical task to examine interactions between micropollutants and develop mostly organism-based ecotoxicity testing for chemical compounds. It is well recognized that a high amount of nanoparticles could lead to significant alternations in the morphology of the algae cells and cause significant ecotoxicity effects (Pereira et al. 2020; Rana and Kumar 2022). Nanoparticles act as primary convey vectors into the ecosystems and promote the entry of nanoparticle-sorbed micropollutants into organism cells and potential toxic impacts (Kahru and Dubourguier 2010; Huang et al. 2022). Furthermore, it also reported that the elevated reactive oxygen species caused growth reduction of algal cell density by about 38%, and their ecotoxicity was associated with the engineered nanoparticles dose and type (Chen et al. 2019).

Perspective

To date, the ecotoxicology response of algae to contaminants has become a growing concern due to their environmental persistence and potential health threats. Our study indicates some significant challenges and future perspectives (Table 2).

  1. 1.

    Microalgae are often used as a model organism in ecotoxicological research owing to ecological relevance, their sensitivity to micropollutants, and their easy culturing and maintenance in laboratory-scale environments. They are deemed helpful tools for studying the effects of pollutants on aquatic ecosystems. To better understand the challenges and opportunities in using behavioral toxicology for regulatory ecotoxicology and threat assessment, future research should include various fields such as behavioral ecology, ecotoxicology, regulatory ecotoxicology, neurotoxicology, and risk assessment and should expand from laboratory studies to field-scale investigations.

  2. 2.

    Research has shown that nano/microparticles in aquatic ecosystems can positively act as critical carriers of chemical compounds and can combine with other pollutants such as heavy metals, persistent organic pollutants, hydrophobic organic chemicals, and others. Therefore, understanding the ecotoxicity of persistent organic pollutants, such as polycyclic aromatic hydrocarbons, toward important marine species would be valuable as open ocean and coastal ecosystems are becoming increasingly polluted globally. Further studies on toxicokinetics are needed to give a higher accurate and sensitive assessment of the risks and threats posed by persistent organic pollutants in aquatic ecosystems and environments.

  3. 3.

    A major challenge in ecological threat assessment is the ability to predict impacts at the community and population level, which are typically the most relevant for protecting aquatic ecosystems. A priority for research is to study the fate and transport of micropollutants in aquatic environments and to explore the mechanisms of how algae respond to ecotoxicity. Scientists need to further examine the influences of environmental conditions and factors on microalgae ecotoxicity. To improve predictions of the potential risks and threats posed by micropollutants to aquatic ecosystems and human health, research on the ecotoxicological effects of these compounds on microalgae must be increased (Lu et al. 2021).

  4. 4.

    The term "ecotoxicology" relates to the potential for physical, biological, or chemical stressors that impact ecosystems. The acute toxicity values showed that the algae application is one of the most sensitive aquatic organism groups (Freixa et al. 2018). However, it needs to be designed to develop the next generation to detect and assess rapid toxicity response. Developing new ecotoxicity tools and/or models for rapidly intelligent quantification of biological impacts and responses of organisms to micropollutants is needed in further studies.

  5. 5.

    The findings demonstrated that pharmaceutical and personal care products could influence algae species and their communities unexpectedly. Besides, the algae also can be used as a helpful model species in aquatic ecotoxicity. The impacts of toxins on the algal population, as well as the indirect effects on higher trophic level organisms, can be applied to investigate to reveal the overall ecotoxicity on the ecosystems. By applying in vitro bioassays, or biomarkers, ecotoxicity properties of environmental samples can be accumulated, and caused ecotoxicological risks could be estimated for monitored ecosystems (De Baat et al. 2019). Ultimately, to overcome these challenges, combining ecotoxicological experiments, tools, and models that give for high-performance will lead to a more comprehensive risk investigation of the influences of chemical stress on ecosystems.

  6. 6.

    It is crucial to have an in-depth understanding and evaluation of how chemical and non-chemical stressors and their mixtures could affect aquatic ecosystems. While there have been notable advancements in the design and development of ecotoxicological tests, significant challenges still need to be addressed before they can be widely used in risk assessments (Schuijt et al. 2021). These challenges include the need for more research on the effects of chemical mixtures on aquatic living forms, the development of sustainable approaches in measuring the impacts of chemicals at the ecosystem and population levels, and the need for better ways to predict the influences of toxic chemicals on the environment. The investigated micropollutants, such as pharmaceutical compounds, were considered as harmful and toxic to the algae. Therefore, to overcome concerns about mechanisms, that means the following approaches need to be introduced to link chemical exposure and its effects in ecological threat assessment.

  7. 7.

    The microalgae-aided technologies should be further integrated flexibly into wastewater treatment plants to make better progress in full-scale (or commercial) applications. Developing low-cost and sustainable wastewater treatment plants approaches to remove pollutants is essential. Considering the environment, microalgae have been attended to and applied extensively (Zhang et al. 2020). These solutions provide relevant and valuable basics that could be applied to excellent strategies for suitable development principles and targeted phytoremediation purposes. Critical green technology with the employment of natural materials is becoming more popular, and this novel method is compatible with the current trend toward sustainable development.

  8. 8.

    Seeking solutions to overcome potential ecotoxicological risks or problems, it is necessary to conduct green technologies for micropollutant remediation. The phytoremediation and microalgae-based approaches are promising solutions for the bioremediation of toxic and persistent compounds such as pharmaceutical and personal care products, heavy metals, nano/microplastics, and pesticides from the environmental matrices (Ky et al. 2020; Leong and Chang 2020; Pessôa et al. 2021; Tomar et al. 2022). Also, it must provide further trends for its application for the bioremediation approach of hydrocarbon-containing compounds. For example, several algae, such as C. vulgaris, could be applied for bioremediation of a polycyclic aromatic hydrocarbon-polluted ecosystem (Tomar et al. 2022).

  9. 9.

    In ecotoxicology research, the influence of environmental conditions or chemicals, e.g., pH, temperature, nitrogen (N), phosphorous (P) levels, and so on, can greatly impact the toxicity of micropollutants that must be noted (Lu et al. 2021). These responses can influence aquatic organisms, particularly algae, which are sensitive, reasonable, and suitable for monitoring and early warning. Responses to chemical compounds and/or environmental stressors can be used as ecological indicators, and indices are frequently applied to investigate the impacts of toxic stressors on the community-scale level. In the future, low-cost approaches should be explored for ecotoxicology, which can significantly contribute toward the Sustainable Development Goals.

Table 2 Challenges, future perspectives, and solutions related to the ecotoxicological response of algae to contaminants in aquatic environments
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Conclusion

This work's findings significantly contributed to improving the understanding of ecotoxicity of various micropollutants, e.g., polycyclic aromatic hydrocarbons, bisphenol A, pharmaceutical and personal care products, per- and polyfluoroalkyl substance, pesticides, heavy metals, and nano/microparticles in an aquatic ecosystem, and the interactions between these micropollutants and their joint toxicity on algae. Reports about the adverse impacts of various pollutants in various algae across trophic chains provide the necessary contribution to encourage the current emergency of ecotoxicity. Algae, especially microalgae, can be applied for investigating and assessing ecotoxicology risks related to pollutants in aquatic ecosystems. This finding indicates several algal strains routinely used in ecotoxicity investigation. They are susceptible to environmental changes and respond quickly to contaminants and/or environmental stressors, making them excellent bioindicators for ecotoxicity assessments, which is indeed a valuable and environmentally friendly approach. Knowledge domain about ecotoxicity and environmental threats; therefore, ecotoxicology needs to be updated for intelligent environmental designing and planning toward Sustainable Development Goals. Furthermore, a novel generation must be developed to examine rapid and accurate ecotoxicity response. It provides the capability that enables cost-effective and fast assessment of the bioavailability and toxicity of micropollutants in ecosystems for government and industry areas. In the future, scientists still need further investigation on ecotoxicity; their mechanisms of emerging pollutants in the environmental matrices should be examined in associated with the mesocosm scale.