Synonyms

Environmental Geochemistry

Definition

Low-temperature or environmental geochemistry is the study of chemical processes that occur in the earth’s surficial environments. While basic aqueous chemistry principles, including acid-base equilibrium, reduction-oxidation reactions, and solubility, are the driving force behind most phenomena, interconnections between geology, hydrology, biology, and atmospheric science require an interdisciplinary approach to investigating these systems. Low-temperature geochemistry is a broad field, but major areas of study include mineral precipitation, chemical weathering, soil chemistry, sedimentary processes and diagenesis, biogeochemical cycles, and contaminant transport.

Introduction to Low-Temperature Geochemistry

In general, geochemistry can be defined as the study of the chemical composition and changes of the earth and other celestial bodies. We further define the subject based upon the overall geologic environment, pressure, or temperature. While the delineations in temperature are somewhat vague, the most accepted definition for low-temperature geochemistry describes the chemistry of minerals, rocks, solid, water, and atmosphere when the temperature is below 200 °C (Guangzhi 1996). This temperature range typically occurs on the earth’s surface or within the first few km of the lithosphere. Surface water, soils, exposed rock formations, groundwater, aquifers, and hydrothermal vents can all be considered systems that are regulated by low-temperature geochemical processes.

Due to the relationship between geochemistry and natural processes that occur within the environment, low-temperature geochemistry is often presented within the context of environmental geochemistry (Ryan 2014). No region on the surface of the earth can be considered a closed system so there are continuous interactions taking place between the various components. Understanding complex environmental systems requires thinking about phenomenon on molecular, regional, and global scales. In addition, it requires using an interdisciplinary approach due to the deep and complex relationship between atmospheric, hydrologic, biotic, and geologic systems (Fig. 1).

Low-Temperature Geochemistry, Fig. 1
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Low-temperature geochemistry requires interdisciplinary thinking due to the interconnections between geology, biology, hydrology, and atmospheric sciences

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Low-temperature geochemistry is also intimately tied to human society because our activities have significant impacts on the processes that are happening on the earth’s surface. Sometimes these activities are direct, such as the release of chemical waste form a mine and milling piles. Other times, the connections are less direct, such as the release of small amounts of a compound that undergo chemical transformations that result in a new compound that has much greater detrimental effects on the ecosystem. Thus a major thrust of low-temperature geochemistry is to understand the impact of humans on these processes on the molecular, regional, and global scales.

History and Basic Principles

Low-temperature geochemistry is a relatively new subdiscipline of geology, developing from the molecular scale before encompassing global phenomena. The Norwegian scientist, Victor M. Goldschmidt is often considered to be the founder of geochemistry with his important contributions to mineral reactivity and his guiding principles on elemental substitutions in crystalline phases (Reinhardt 2001). The idea of geochemistry was broadened by the work of Vladimir I. Vernadsky, who determined that chemical reactions resulted in the formation of minerals and more specifically that living organisms could reshape geological systems or even planets (Ryan 2014). Investigations regarding the consequences of anthropogenic activities on environmental and geochemical systems began in the 1960s with concerns regarding contamination of the air, water, and soil. Seminal work during this period found that pesticides were a significant threat to ecosystem health (Carson 1962), acid rain was caused by industrial emissions (Likens and Bormann 1974), and humans were impacting the global climate through emissions of greenhouse gasses (Hansen et al. 1981). Current investigations in low-temperature geochemistry span the range of topics and scale that was laid down by the leaders in this area.

At the most basic level, low-temperature geochemical processes are controlled by fundamental chemical principles that control reactions in aqueous systems (Fig. 2). A major factor in the formation and dissolution of minerals and rocks is acid-base equilibrium and hydrogen ion activity (pH). In water, the hydrogen ion activity (pH) is the driver for many geochemical properties including dissolution, precipitation, crystallization, gas solubilities, and biochemical reactions. The pH of the solution can also be influenced by inorganic constituents, most notably the equilibrium between dissolved carbon dioxide and the carbonate anion (Drever 1997). Reduction and oxidation (redox) reactions are also of importance for elements that can access multiple oxidation states. Hydrogen, nitrogen, oxygen, sulfur, iron, and manganese are abundant and important redox active elements in geochemical systems (Drever 1997). These elements typically control the redox conditions within aqueous solutions, which in turn can determine the speciation, mobility, and toxicity of trace metals and organic compounds. Organisms, such as microbes and fungi, also play an important role in harnessing the chemical energy within geochemical systems to control the redox conditions, molecular speciation, and precipitation of mineral phases. Equilibria between the various inorganic and organic components and their overall energetics and stability (thermodynamics) ultimately determine the overall chemical reactions and products within the environment (Drever 1997). These basic chemical principles can be applied to a wide range of geologic media, environments, and processes, and the broad categories of low-temperature geochemistry will be described in the following sections.

Low-Temperature Geochemistry, Fig. 2
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Fundamental chemical reactions, such as acid-base, reduction-oxidation, and crystallization/precipitation, control low-temperature geochemical processes

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Major Topics in Low-Temperature Geochemistry

Mineral Precipitation/Crystallization and Chemical Weathering

A wide range of common mineral phases is formed under low-temperature geochemical conditions by precipitation and crystallization reactions. Precipitation is the direct result of reaching the solubility limit of an aqueous species that leads to the formation of a solid phase (Jarvinen 2009). Crystallization can be considered a precipitation reaction, but more specifically, one that has long-range ordering of the chemical constituents within the crystalline lattice. Amorphous phases may form from precipitation reactions, but minerals must have some degree of crystallinity (Jarvinen 2009). Table 1 provides a summary of common mineral classes and phases that form under low-temperature geochemical environments, although there are a number of less abundant minerals that form under similar conditions. The major mineral types that typically form in surficial or hydrothermal environments include hydroxides, borates, carbonates, halides, sulfides, and clays (Klein 2002).

Low-Temperature Geochemistry, Table 1 Common mineral classes and phases formed from low-temperature geochemistry processes
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Changes in chemical equilibria related to pH or redox conditions or through the evaporation of water can result in the precipitation of aqueous species into a solid mineral. Acidic waters can dissolve metal cations, such as Fe(III) and Al(III) and upon mixing with more neutral freshwater, causes the formation of hydrolysis products. These hydrolysis products have low solubility in water and cause the precipitation of hydroxide phases (Stumm and Morgan 1981). In some cases, the metal cation is present in the reduced form, and initial oxidation is required for the precipitation reaction to occur. Such is the case for dissolved Fe(II) oxidizing in the presence of O2 to form Fe(III), which is then followed by the hydrolysis and precipitation reaction (Stumm and Morgan 1981; Cornell and Schwertmann 2004). Evaporite minerals are formed when saline lakes or restricted sea bodies evaporate, creating extensive deposits in arid regions (Schreiber and Tabakh 2000; Klein 2002). Halides and sulfates are the most common evaporite mineral classes, with gypsum and halite deposits constituting the most common mineral species within the natural deposits (Spencer 2000; Screiber and Tabakh 2000). Carbonates can be marine in origin, and over the history of the earth there has been a shift from low-temperature chemical precipitation to biogenic sources, such as benthic and pelagic organisms (Morse et al. 2007). Calcium carbonate is also a major constituent in freshwater systems and is widely observed in sedimentary rocks and as the building blocks of cave formations (Drever 1997; Klein 2002; Kotz et al. 2006; James and Jones 2015). Borate mineral deposits can be found in marine basins, but the largest known deposits originated as chemical precipitates from thermal springs or hydrothermal solutions associated with volcanic activities (Kistler and Smith 1975; Argust 1998).

Chemical weathering is the change in the composition of the original geologic media, often in the presences of water that occur because of oxidation, hydrolysis, and dissolution of the elements present in the parent rock (Carroll 1962). Some hydroxide phases, like bauxite, form in surficial or low-temperature supergene environments by leaching of silica from aluminum-bearing rocks (Schellmann 1994). The leaching process occurs through initial dissolution of the mineral lattice by the slightly acidic rainwater, followed by hydrolysis and precipitation of the insoluble hydroxide phase upon an increase in the pH of the pore water (Whittington and Muir 2000). Hydrolysis reactions occur when anhydrous mineral absorbs water and water dissociates to H+ and OH− ions, which interact with the cations present in the solid and result in structural changes to the solid-state material (Reaction Scheme 1). Overall the reaction causes the formation of a secondary mineral phase from the parent rock, plus soluble species that are removed as the water flows over the surface. Other hydroxide phases, such as goethite and ferrihydrite, can form from an initial oxidation step, such as the oxidation both sulfur and iron in pyrite, followed by hydrolysis and precipitation (Lowson 1982; Nordstrom 1982). Dissolution reactions result in the breakdown of the solid-state mineral into soluble aqueous species. One of the most common mechanisms for dissolution occurs when CO2 in the atmosphere is dissolved in rainwater to form carbonic acid, which is also referred to as carbonation reactions (Reaction Scheme 3) (Ryan 2014).

$$ {\displaystyle \begin{array}{c}\hfill \mathrm{Reaction}\ \mathrm{Scheme}\ 1\ \left(\mathrm{Hydrolysis}\right)\hfill \\ {}\hfill 2\ {\mathrm{K}\mathrm{AlSi}}_3{\mathrm{O}}_8\left(\mathrm{s}\right)+2\ {\mathrm{H}}^{+}\left(\mathrm{aq}\right)+9\ {\mathrm{H}}_2{\mathrm{O}}_{\left(\ell \right)}\to {\mathrm{H}}_4{\mathrm{Al}}_2{\mathrm{Si}}_2{\mathrm{O}}_{9\left(\mathrm{s}\right)}+4\ {\mathrm{H}}_4{\mathrm{Si}\mathrm{O}}_{4\left(\mathrm{aq}\right)}+2\ {{\mathrm{K}}^{+}}_{\left(\mathrm{aq}\right)}\hfill \end{array}} $$
$$ {\displaystyle \begin{array}{c}\hfill \mathrm{Reaction}\ \mathrm{Scheme}\ 2\ \left(\mathrm{Oxidation}\right)\hfill \\ {}{\mathrm{FeS}}_{2\left(\mathrm{s}\right)}+15/4\ {\mathrm{O}}_{2\left(\mathrm{aq}\right)}+7/2\ {\mathrm{H}}_2{\mathrm{O}}_{\left(\ell \right)}\to \mathrm{Fe}{\left(\mathrm{OH}\right)}_{3\left(\mathrm{s}\right)}+2\ {\mathrm{H}}_2{\mathrm{SO}}_{4\left(\mathrm{aq}\right)}\hfill \end{array}} $$
$$ {\displaystyle \begin{array}{c}\hfill \mathrm{Reaction}\ \mathrm{Scheme}\ 3\ \left(\mathrm{Dissolution}/\mathrm{Carbonation}\right)\hfill \\ {}\hfill \phantom{\rule{0ex}{1em}}{\mathrm{CO}}_{2\left(\mathrm{aq}\right)}+{\mathrm{H}}_2{\mathrm{O}}_{\left(\ell \right)}\to {\mathrm{H}}_2{\mathrm{CO}}_{3\left(\mathrm{aq}\right)}\hfill \\ {}\hfill \phantom{\rule{0ex}{1em}}{\mathrm{Ca}\mathrm{CO}}_{3\left(\mathrm{s}\right)}+{\mathrm{H}}_2{\mathrm{CO}}_{3\left(\mathrm{aq}\right)}\to {{\mathrm{Ca}}^{2+}}_{\left(\mathrm{aq}\right)}+2\ {\mathrm{H}}_2{\mathrm{CO}}_{3\left(\mathrm{aq}\right)}\hfill \end{array}} $$

Sedimentary Processes and Diagenesis

Chemical weathering results in the breakdown of rocks and formation of soils, but sedimentation processes utilize geochemical reactions to create new geologic deposits. Sedimentary rocks are formed by the accumulation of sediments (small particles of gravel, sand, silts, and clays) that are held together through lithification (West 1995). Early diagenesis or lithification is the process by which unconsolidated sediments are converted into solid rock and can occur via mechanical (compaction), geochemical (cementing or crystallization), or a combination of both processes. Cementation involves filling the pore space between the individual sediment grains with a binding agent. Under low-temperature regimes, calcium carbonate or iron hydroxides can precipitate from water seeping through the sediments, resulting cementation and lithification to occur (West 1995). Crystallization processes typically focus on the transformation of amorphous or colloidal substances into crystalline mineral phases and generally occur after deposition and even in some cases after lithification of the sedimentary rock.

Changes in the sedimentary rocks at temperatures and pressures lower than the formation of metamorphic rocks is considered late diagenesis (Teodorovich 1961). It is important to point out that late diagenensis is a different process than chemical weathering described above. Recrystallization processes can occur during later diagenesis, most notably in limestones, where aragonite in contact with freshwater can convert into calcite crystals within the solid sedimentary rock. Burial of organic matter within sedimentary rocks results in the chemical transformations of lipids, proteins, carbohydrates, and lignin-humic compounds into hydrocarbons, which are the major constituents of methane, petroleum, and coal deposits (Singer and Muller 1983).

Chemistry of Soils

Low-temperature geochemical processes are the driving force for the formation and evolution of soils in the surficial environments. Soils are porous media created at the surface by weathering processes and differ from weather rocks because they show a vertical stratification (Sposito 1989). Mechanical weathering processes can result in the breakdown of bulk rock into smaller particles and is combined with chemical weathering processes to form the inorganic components of soils (Sposito 1989). Given the presence of water and dissolved chemical components, soils are excellent environments for microbes and fungi that can control redox reactions and breakdown organic matter (Ehlrich and Newman 2009). This leads to a complex mixture of organic components that are hospitable to plants and larger organisms and a rich and diverse biogeochemical system.

Soils are in continuous flux and exchange both matter and energy with the surrounding air, water, and biome (Sposito 1989). Meteoric water is continually percolating through soils, dissolving soluble chemical species, and transporting it through the soil column. Atmospheric gasses can easily penetrate this porous media, resulting in additional weathering and oxidation reactions (Sposito 1989). Microbial communities can continuously evolve through changes in the chemical and physical conditions of the soil (Ehlrich and Newman 2009). Humans can also influence the soil environment, either directly (intensive agricultural efforts) or indirectly (acid rain), and in turn the soil quality has impacts on overall health of the population (Locke and Zablotowicz 2004; Singh and Agrawal 2008; Brevik and Sauer 2015).

Biogeochemical Cycling

The surficial environment can be considered an open system with continual chemical fluxes between the various components; thus there is continuous movement of elements throughout the global system (Schlesinger 1997). As discussed in the previous sections, meteoric water moves through soils and porous rocks, picking up various chemical components through weathering processes. Some of the chemical constituents in the water can undergo precipitation reactions within the soil or porous rock, resulting in a sink or removal of that particular element from the solution. Interactions with plants and organisms can also cause elements to either remain in the soil or biome or be transported with the hydrologic flux. Other elements can remain dissolved in the water, where it is transferred through the subsurface system and can then be recharged into surface water through seeps and springs. Additional precipitation or redox reactions can occur within the surface water either resulting in precipitation or dissolution of the chemical component, where there can again be interactions with biological systems or dispersion into the atmosphere. Once in the atmosphere, additional chemical reactions can occur that result in addition global dispersion or wet/dry deposition. The impact of human activities must also be accounted for when considering the flux of elements between the biological, geological, hydrological, and atmospheric systems. It is the chemical reactions that occur within these systems combined with the flow and mass balance of elements of interest within these different domains that constitutes the study of biogeochemistry (Schlesinger 1997).

A well-known biogeochemical cycle as illustrated in Fig. 3, which describes the different chemical processes that control the flux of nitrogen throughout the soil, ocean, and atmosphere (Schlesinger 1997). A portion of the nitrogen is stored as a reservoir within the organic matter of the soil that can undergo chemical reactions, such as mineralization (Reaction Scheme 4) and nitrification (Reaction Scheme 5). Within the soil column, nitrogen is also involved with an internal cycle of uptake and release within terrestrial plants and additional mass is added to the soil through biological fixation (Reaction Scheme 6). Removal of nitrogen from the soil can occur through denitrification (Reaction Scheme 7) and release to the atmosphere. A second pathway for release is the dissolution of the nitrogen in the form of NO3−(aq) or NH4+(aq) that can be transported either by the subsurface groundwater or as run-off into freshwater streams, rivers, and lakes. Eventually the water from the surface and subsurface sources flow into the ocean where there is a large reservoir of dissolved nitrogen species. An internal cycle also occurs in the ocean with the uptake and release of nitrogen by phytoplankton and marine organisms and burial in the ocean sediments. Flux to the ocean can also occur through nitrogenase-catalyzed biological fixation, and removal of nitrogen to the atmosphere occurs through denitrification processes (Kim and Reese 1994). Within the atmosphere, nitrogen can be converted to different forms through fixation by lightning or photocatalyzed redox reactions. Humans can also add to the global nitrogen cycle through release of NOx gasses or through the overfertilization of agricultural lands (Fields 2004). Changes in the amount of nitrogen in the air or freshwater systems that is the result of human activity can cause significant changes in the nitrogen reservoirs for these systems. This has impacts on the state of these systems as evidenced by the production of acid rain or the eutrophication of the coastal regions, particularly the Gulf of Mexico (Schlesinger 1997; Fields 2004).

Low-Temperature Geochemistry, Fig. 3
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The biogeochemical cycle for nitrogen. Values are provided by Schlesinger (1997) and are in units of 1012 g N per year

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$$ {\displaystyle \begin{array}{l}\mathrm{R}\mathrm{eaction}\ \mathrm{Scheme}\ 4\ \left(\mathrm{mineralization}\right)\\ {}\mathrm{R}-{\mathrm{NH}}_2+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{NH}}_3+\mathrm{R}-\mathrm{OH}\end{array}} $$
$$ {\displaystyle \begin{array}{c}\hfill \mathrm{Reaction}\ \mathrm{Scheme}\ 5\ \left(\mathrm{nitrification}\right)\hfill \\ {}{\mathrm{NH}}_3+\frac{1}{2}{\mathrm{O}}_2+2{\mathrm{e}}^{-}\to {\mathrm{NH}}_2\mathrm{O}\mathrm{H}+{\mathrm{H}}_2\mathrm{O}\to {{\mathrm{NO}}_2}^{-}+5\ {\mathrm{H}}^{+}+2\ {\mathrm{e}}^{-}\hfill \end{array}} $$
$$ {\displaystyle \begin{array}{l}\mathrm{Reaction}\ \mathrm{Scheme}\ 6\ \left(\mathrm{nitrogen}\ \mathrm{fixation}\right)\\ {}{\mathrm{N}}_2+8{\mathrm{H}}^{+}+6{\mathrm{e}}^{-}\to 2{{\mathrm{N}\mathrm{H}}_4}^{+}\end{array}} $$
$$ {\displaystyle \begin{array}{l}\mathrm{Reaction}\ \mathrm{Scheme}\ 7\ \left(\mathrm{denitrification}\right)\\ {}2\ {{\mathrm{N}\mathrm{O}}_3}^{-}+12{\mathrm{H}}^{+}+10\ {\mathrm{e}}^{-}\to {\mathrm{N}}_2+6{\mathrm{H}}_2\mathrm{O}\end{array}} $$

Changes that human activity has on global biogeochemical cycles for a wide range of elements are a major area of current scientific investigations. Global warming is the direct result of changes in the carbon cycle, and understanding the details of the chemical reactions that result in fluxes between the different systems is important for more accurate climate models and means for combating climate change (Hansen et al. 1981). As described above, overfertilization of agricultural lands causes an influx of elements that are then washed into freshwater rivers in lakes. While excess nitrogen causes problems in marine environment, the high influx of phosphorus results in the eutrophication of freshwater systems (Correll 1998). Human activity can also influence the global cycling of trace metals due to their use in industrial applications or modern living and then release through improper disposal. Lead (Pb) is an example a trace metal that was impacted by anthropogenic effects when it was added as a fuel additive in the 1970s (Shotyk and Le Roux 2005). During the combustion process, lead was released into the atmosphere through exhaust systems that resulted in dry and wet deposition into surface waters and land. Increased concentrations of lead were observed in soils and the human population until polices were adopted that minimized the use of lead as an additive and in industrial processes (Shotyk and Le Roux 2005).

Contaminant Transport

Low-temperature geochemical processes control the oxidation state and speciation of elements that are harmful to human and ecosystem health, which in turn determines the mobility and fate of contaminants in the environment. Release of contaminants into the environment can be through natural processes or through human activities that catalyze the release of toxic elements and compounds into the environment (McCarthy and Zachara 1989; Brown and Calas 2011). For example, weathering and dissolution of host rocks can occur either through natural ore deposits that are exposed to the atmosphere or groundwater or the leaching from mine and milling tailings. Typically this process is controlled both by the acid-base chemistry of the meteoric water and redox reactions when the rocks are exposed to oxygen present in the atmosphere. Mobility of the contaminant phases in surface or subsurface waters depends on the aqueous speciation and water-rock interactions. Surface interactions typically involve adsorption and binding of the contaminant to mineral phases, which can limit its mobility in the environment (McCarthy and Zachara 1989; Brown and Parks 2001). Contaminant adsorption on mineral surfaces can be reversible and again controlled by the low-temperature geochemical parameters. Interactions with the microbial community can also impact the fate of contaminants in soils and sediments, typically by control of redox parameters and precipitation reactions (McCarthy and Zachara 1989; Ehrilich and Newman 2006). Ultimately the chemical speciation controls the mobility of the contaminant in water, uptake by biological organisms, and the overall public health risk.

Inorganic elements that are of concern for public and ecosystem health include heavy metals, radioactive isotopes, and problematic main group elements. Heavy metals, such as mercury, are naturally occurring elements that become contaminants in the environment due to natural processes (redox, microbial activity) but can also be caused by human activities, such as mining, release from industrial processes, or accidental dispersion. Speciation of mercury is a major factor in determining health risk, with methylation by bacterial communities resulting in increased uptake and bioaccumulation (Boening 2000). Arsenic is an example of a problematic main group element that occurs naturally and becomes soluble when in the reduce form (arsenite, AsO33−) (Bowell et al. 2015). Countries such as Bangladesh, India, China, Mexico, and Argentina have significant arsenic contamination in water sources due to formation of strongly reducing aquifers or closed basins in arid or semiarid climates (Smedley and Kinniburg 2002). Uranium is a naturally occurring radioactive element that has health risks when ingested through drinking water or food sources due to its chemical and radiological toxicity (Brugge et al. 2005). Redox conditions also drive the mobility of uranium in environmental systems, with the oxidize uranyl (UO22+) moiety forming soluble complexes over a range of environmentally relevant pH values (Maher et al. 2013).

Organic contaminants are typically the result of human activities and can be controlled by natural geochemical processes that are often utilized by environmental remediation. Volatile organic compounds, plasticizers, pesticides, and chlorinated compounds are the most common organic pollutants in drinking waters (Olson 2003). Due to concerns over the presence of hormones and endocrine disruptors, the USGS comprehensive survey conducted in 2002 also that found steroids (coprostanol, cholesterol), insect repellant (N,N-diethyltoluamide), caffeine, antimicrobial agents (triclosan), fire retardant (tri(2-chloroehtyl)phosphate), and detergent residues (4-nonylpentol) can be detected in surface waters and are now considered emerging contaminants (Kolpin et al. 2002; Lapworth et al. 2012). Sunlight can cause photochemical reactions that transform natural organic matter into other compounds, such as halogenated species (Mendez-Diaz et al. 2014). Some of these transformations can yield degradation products that are less harmful than the initial material, but some of these reactions were reported to be reversible. An endocrine disruptor, 17α-trembolone has been shown to degrade in the presence of light but then reform in the dark (Qu et al. 2013). Chemical spills of hydrocarbons or chlorinated compounds present in groundwater can be remediated through microbial degradation processes that utilize these compounds as an energy source. For example, tetrachloroethane and trichloroethane are common contaminants in water, but under anerobic conditions microbial communities can be transformed to less chlorinated dichloroethane and vinyl ethane for natural attenuation (Bradley et al. 2005).

Summary

Low-temperature geochemistry is the study of chemical processes that occur in a complex and ever changing environment. It requires understanding fundamental chemical principles applied to geology, hydrology, biology, and atmospheric systems to understand some of the most important processes on the surface of the earth. Mineral precipitation, chemical weathering, sedimentation, diagenesis, soil science, biogeochemical cycling, and contaminant transport impact natural ecosystems and human society. Low-temperature geochemistry also provides a means to understand how interconnected we are with natural processes and our actions can cause significant impacts on global processes.

Beginning with fundamental elemental processes that occur within solid-state minerals and branching out into global topic, low-temperature geochemistry continues to be an important area of scientific study. Continued interest in combating climate change requires advanced understanding of how rocks, soils, natural bodies of water, and the atmosphere are connected through chemical, physical, and biological processes. As we continue to change the landscape and release new chemicals into the environment, there is increased efforts to determine the impact of these emerging contaminants on the ecosystem. Given our relationship and reliance on the natural world, understanding the geochemical processes that occur in low-temperature, surficial environments will continue to be a key research focus for human and global health.

Cross-References