1 Introduction

Consumable milk is one of the main forms of animal protein often obtained from animals such as buffalo, cow and goat. Milk production is a distinctive feature of the female animals and human being because they possess the udder and the breast, respectively which contains the mammary gland [1]. Milk is highly consumed by human beings at all stages of life because it serves as a reliable source of energy, fat, minerals, vitamins and proteins [2].

A good number of evaporated milk products are available in Nigeria markets with the raw milk coming from the dairy farm. The primary source of such milk products (the cows) are often allowed to graze over a wide expanse of land such as the farm lands and the forest since open grazing is more economical. More often than not, these cows have direct contact with agricultural products and sometimes feed on farm produce during such open grazing. Beyond this, the cows are fed from streams and rivers which are sometimes not too distant from the grazing region.

Between 1948 and 1949, synthesized chemicals were of great relevance starting with the use of dichlorodiphenyltrichloroethane (DDT) for malaria control and hexachlorocyclohexane (HCH) for locust control. Dichlorodiphenyltrichloroethane was effective for malaria control in the 1940s. It showed a decisive role in the eradication of malaria from Europe and the United States. Within a short time, DDT got a unique position by saving millions of lives and by preventing disease outbreaks much more than any other man-made chemicals in history [3]. A huge success was recorded in the use of these organochlorine pesticides (OCPs) up to 1980 when suggestions were made for controlled usage of OCPs because of the serious health risks such as cancers, endocrine disruption, immune system disorder, reproductive problems among other chronic diseases that could emanate from their persistence or high resistance under ambient environmental conditions [4]. Increase in agricultural productivity and the affordable price of these pesticides were the major considerations of farmers. Hence, the drastic increase in the application of these substances to agricultural produce all over the developing world despite the public health risks and outcries that have led to their being banned in developed countries [5]. Unfortunately, less than one percent of the applied pesticides in agriculture usually reach the target pest while the remainder is stored in the various compartments of the environment [6]. For example, upon application, most part of the pesticides volatilize from the soil are transported to non-target components [7], penetrate into the soil through percolation-related phenomena, get to aquatic bodies through run-off [8, 9], and aerial fall-out especially as a result of wet precipitation [7, 8].

The main entry points of pesticides into biotic factors include contaminated feed, water and udder. Quite a number of studies have confirmed the presence of these OCPs in water bodies in various countries of the world such as Nigeria [10,11,12,13], Ghana [14], South Africa [15] and China [16]. Pesticides find their way into meat and milk as a result of open grazing of animals on contaminated feedstock prior to milking and thus may enter the upper echelon of the food chain where they bioaccumulate as a result of their lipophilicity [17]. Contamination of milk with organochlorines such as Hexachlorocyclohexane (HCH) isomers, Dichlorodiphenyltrichloroethane (DDT) and isomers, Heptachlor, Chlordane, Aldrin, Dieldrin and so on (Fig. 1) may cause neurodevelopment delay [18], reproductive defects, preterm and immune toxicity [19, 20].

Fig. 1
figure 1

Structure of common organochlorine pesticides

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Evidently, awareness about the levels, health impacts and reduction or total removal of xenobiotics such as OCPs from human consumables is both a matter of necessity and urgency. A number of methods have been employed for the quantitative detection of OCPs in water and other consumables [9, 21]. The bulk of these methods are chromatographic techniques coupled to suitable detectors such as the electron capture, thermal conductivity and mass spectrometry [21,22,23]. Selectivity and specificity for analytes [24], ability to characterize such analytes [25], availability and cost of instrumentation are the major factors considered for selecting a suitable chromatographic technique for the quantification and identification of OCPs in various matrices. These factors, coupled with the high vapour pressure of OCPs have made the use of Gas Chromatography (GC) coupled to Mass Spectrometry (GC–MS) a highly preferred technique for OCPs determination [26]. Although, the more expensive GC coupled to a tandem Mass Spectrophotometer (GC–MS-MS) is considered more sensitive [23], meticulous sample preparation processes involving LLE technique followed by clean-up that reduces matrix effect prior to quantification helps to mitigate the lower sensitivity of the GC–MS [27, 28] and bridge the gap in effectiveness between the liquid–liquid extraction and microextraction.

The present study was aimed at investigating the content of OCPs in six popularly consumed evaporated milk products in Nigeria. This was done to provide reliable scientific data bothering on the possible carcinogenic and non-carcinogenic health risks associated with their long-term consumption. The novelty of this work is that most of the previous studies were based on evaluation of OCPs in randomly selected milk brands. However, a preliminary survey based on respondents randomly interviewed prior to sample collection to determine the consumers’ choice as regards commonly consumed evaporated milk were used for the choice of the samples used for this study.

2 Methodology

2.1 Sample Collection

The response of 210 respondents randomly interviewed prior to sample collection to determine the consumers’ choice as regards commonly consumed evaporated milk samples in Nigeria informed the selection of the six types of evaporated milk samples eventually used for this study. The milk samples (coded A–F) were purchased from sales outlets within Ile-Ife environment and kept in a refrigerator prior to the extraction to achieve a storage temperature of about 4οC.

2.2 Reagents Used and Their Sources

Reagents such as ethanol, acetone, dichloromethane (DCM) and sodium chloride used for this procedure were supplied by GFS Chemicals, Columbus. Silica gel was supplied by Labtech chemicals while the anhydrous sodium sulphate was supplied by Merc, Germany. They were all of analytical grade.

2.3 Extraction of OCP Residues from Samples

Five millilitres (5 mL) of each sample was transferred into 500 mL volumetric flask and thoroughly mixed with about 100 mL distilled water. One spatula of sodium chloride was then added to make OCPs less soluble in the aqueous layer and more readily available for DCM extraction. The mixture was diluted up to 500 mL in the flask and subjected to thorough mixing. Each component of the solvent extraction setup was washed and rinsed properly with the solvent mixture (1:2:2 of Acetone-Dichloromethane-Ethanol). A 500 mL separating funnel was used to carry out the LLE of the diluted milk sample in which case half of the separating funnel was filled with the diluted sample and extracted with about 20 mL DCM in triplicates. This process was carried out for the other half of the diluted milk sample. The extracts were transferred into an amber coloured vial and stored at 4 °C in readiness for clean-up.

2.4 Clean-Up Procedure

The clean-up stage is essential to remove or reduce all forms of impurities which might be associated with the eluate. A column was packed with glass wool followed by the addition of activated silica gel earlier prepared in a slurry form. Anhydrous sodium sulphate was then added to the top of the silica gel in order to absorb the water in the sample and the solvent. Dichloromethane was first introduced into the packed column to prevent any interference by organic contaminants. The recovered eluate was left to dry completely under ambient air and then reconstituted with 1 mL of n-hexane in the amber coloured vials prior to GC–MS determination.

2.5 Instrumental Analysis, Quality Assurance and Quality Control


The qualitative identification and quantification of the OCPs was carried out using the GC–MS at CTX-ION Analytical Limited, Ikeja, Lagos, Nigeria. The efficiency of this analytical procedure was validated by recovery analysis since a certified reference material was unavailable. A standard solution of mixture of Heptachlor, Endrin, Endosulfan and p,p′-DDT was prepared and 10 mL of this solution was used to spike the measured value of milk sample (5 mL) while the equivalent milk volume (5 mL) was kept unspiked. These two milk samples were taken through the extraction, clean-up and reconstitution procedures as enumerated earlier. The samples were subjected to GC–MS analysis and percentage recovery (% R) was evaluated using Eq. 1.

$$ {\text{\% R}} = \frac{{\left( {{\text{A}} - {\text{B}}} \right)}}{{\text{C}}}{ } \times { }100 $$
(1)

where A and B are the amounts of OCPs recovered from spiked and unspiked samples respectively; and C represents the amount of OCPs used for spiking. In order to achieve reliable results, the quality assurance of the analytical procedures was given special attention. All materials for sample preparation were thoroughly washed and rinsed with acetone. Blank determination was equally carried out. All reagents used were of analytical grade.

2.6 Health Risk Assessment

Carrying out the health risk assessment is important to assess the health risks associated with dietary exposure of consumers to pesticides content of the milk samples. This was done by investigating the carcinogenic and non-carcinogenic health risks through the Estimated Average Daily Intake (EADI), Cancer Benchmark Concentrations (CBC) and the Health Risk Index (HRI). Estimated Average Daily Intake of the pesticides was used to obtain the long term health risk associated with contaminated food consumption, HRI was used for the assessment of the carcinogenic and non-carcinogenic health risk with an assumption of body weights of 60 kg and 16.7 kg for adults and children, respectively [21]. The carcinogenic effect of each of the OCPs was obtained from the Hazard Ratio (HR) calculated using CBC.


Estimated Average Daily Intake was determined by multiplying the Residual pesticide concentrations of each OCP (µg/g) by the food consumption rate (kg/day) and dividing by body weight. Calculations were performed for adults and children who were considered to have average weight of 60 kg and 16.7 kg, respectively at a consumption rate of 0.00983 kg/day of milk [29].

$$ {\text{EADI}} = \frac{{F \times {\text{Cr}}}}{{{\text{Mean}}\;\;{\text{body}}\;{\text{weight}}}} $$
(2)

where F = food consumption data and Cr is the concentration of the residue in the food sample. Samples with HRI > 1 are classified toxic and unsafe for consumption [29].

$${\text{HRI }} = { }\frac{{{\text{EADI}}}}{{{\text{ADI}}}}$$
(3)

where ADI is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime [30].


The Cancer Benchmark Concentration (CBC) was calculated using the formula of [31] stated as:

$${\text{CBC }} = { }\frac{{\left( {{\text{RL}}/{\text{OSF}}} \right){ } \times {\text{ Bw}}}}{{{\text{CR}}}}$$
(4)

where RL is the maximum acceptable risk level (1 × 10–6), OSF is the Oral Slope Factor (mg/kg/day), Bw is the body weight (kg) and CR is the consumption rate (kg/day). The CBC for carcinogenic effect is derived by setting the risk to one in one million due to lifetime exposure. The OSFs for the pesticides were obtained from [32]. The Hazard Ratio (HR) was determined to evaluate the carcinogenic potency of each sample with respect to each OCP using Eq. 5.

$${\text{HR }} = { }\frac{{{\text{EADI}}}}{{{\text{CBC}}}}$$
(5)

3 Results and Discussion

The reliability of the analytical procedures adopted was tested in terms of percentage recovery (%R) and the values obtained are as shown in Table 1 With percentage recovery values of 89.92% of Hepachlor to 96.34% of Endosulfan, the analytical procedure was believed to be efficient to produce reliable results since the %R values of the OCPs fell within the [33] acceptable range of 70–110%.

Table 1 Percentage recovery of OCPs
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The concentrations of organochlorine pesticides (OCPs) in the six (6) different milk samples obtained using Gas Chromatography–Mass Spectrometry (GC–MS) are summarized in Table 2.

Table 2 Concentrations (µg/mL) of OCPs in analysed evaporated milk samples
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The results obtained from the study indicated that three major classes of OCPs (Hexachlorocyclohexane, HCH; Dichlorodiphenylethanes; and Cyclodienes) were detected. The highest total concentrations of OCPs (39.010 µg/mL) were recorded in sample C in which OCPs levels fell within the range of below detection limit (BDL) of Endosulfan sulphate and Heptachlor epoxide to 10.020 µg/mL of Endrin ketone, while the lowest total concentrations of OCPs (21.632 µg/mL) were found in Sample B with individual OCPs concentrations also ranging from BDL of Endosulfan sulphate and Heptachlor epoxide to 5.228 µg/mL of Heptachlor. The level of OCPs in the milk samples have been pictorially demonstrated in Fig. 2.

Fig. 2
figure 2

OCP contents of evaporated milk sample

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Aldrin levels in the samples ranged from 0.414 µg/mL in sample A to 2.468 µg/mL in sample C. The International Agency for Research and Cancer (IARC) classified Aldrin as a Class 2B Carcinogen [34]. All the milk samples contained levels of Aldrin exceeding the designated ADI value (0.0001 µg/g/day) for Aldrin in food [35]. Dieldrin occured at levels that ranged between 1.882 µg/mL in sample A to 8.330 µg/mL in Sample F. Aldrin is readily converted to Dieldrin under ambient environmental conditions and in the body system [9]. Thus, the levels of Dieldrin detected in the samples might be as a result degradation of Aldrin to Dieldrin. Also, all the milk samples contained amounts of Dieldrin exceeding the designated ADI value (0.0001 µg/g/day) for Dieldrin in food [35]. Hence, consumption of these milk samples should not be too regular. The maximum amount of Dieldrin and Aldrin reported in this study are much lower than the values of 10.4 mg/kg and 59.9 mg/kg, respectively, reported by [36] for the leaf samples of cabbage from selected agricultural area in northern Nigeria but higher than the values reported by Adeleye et al. [21] for Amaranths (0.205 and 0.509 mg/kg, respectively) and Fluted pumpkin (1.465 and 0.391 mg/kg, respectively) leaf samples obtained from south-western Nigeria.

Endosulfan is a mixture of two stereoisomers, ɑ-Endosulfan (Endosulfan I) and β-Endosulfan (Endosulfan II) in ratio 70:30, respectively with the former being the most toxic [37]. Endosulfan I showed levels ranging from 0.620 µg/mL in sample B to 4.230 µg/mL in sample D. The recommended ADI value for Endosulfan I in foods is 0.006 µg/g/day [38]. In some studies in animals, Endosulfan induced alterations in the testes and reduced the amount and quality of sperm [39]. It is equally implicated in the reduction of the level of testosterone in the blood [40]. Animal studies have shown that swallowing Endosulfan in contaminated food over long periods affects mainly the kidneys [41]. The milk samples investigated contained levels of Endosulfan I exceeding the designated ADI value (0.006 µg/g/day) for Endosulfan in food [38]. Compared to the level of Endosulfan I in cocoa bean samples (ND—12.11 µg/g) collected by Oyekunle et al. [9] from south-western Nigeria, the Endosulfan I content in sample D can be considered much lower. Similarly, Endosulfan II showed levels with a range of 0.432 µg/mL in sample E to 1.786 µg/mL in sample F. These values were equally beyond the recommended ADI value for Endosulfan in food but much lower than the values obtained by Oyekunle et al. [9] from cocoa beans (ND—49.29 µg/g) collected from Ondo State in South-western Nigeria. People exposed to high levels of Endosulfan in contaminated food or exposed during field spraying suffered tremors and seizures while some died [41]. Endosulfan sulfate is a product of oxidation and the major metabolite of Endosulfan. Compared to the stereoisomers of endosulfan, endosulfan sulphate is the most persistent. Endosulfan sulphate showed levels with a range of BDL in sample B and C to 1.056 µg/mL in sample A. This Endosulfan sulfate level is much higher than the ADI value (0.006 µg/g/day) for Endosulfan sulphate in foods but much lower than the values reported by Oyekunle et al. [9] for cocoa beans (0.48–48.04 µg/g) collected from Osun State, Nigeria. Tremors and seizures, including systemic effects which may be secondary to the seizures have been reported for acute Endosulfan exposure [41].

It has been established that exposure to Endrin can cause various harmful effects including headache, dizziness, nervousness, nausea, vomiting, convulsions, severe CNS injury or damage and death [42]. In the milk samples, levels of Endrin ranged from BDL in samples D and F to 0.176 µg/mL in sample A. The assigned threshold value for daily intake for Endrin (ADI value) is 0.0002 µg/g/day [35]. Levels beyond the designated ADI values were observed for samples A, B, C and E. The level of Endrin in sample A was very close to that obtained from green algae (0.18 µg/mL) of a riverine ecosystem of South-South part of Nigeria in a study carried out by [43]. Levels of Endrin aldehyde ranged between 3.114 µg/mL in sample E to 10.412 µg/mL in sample D. The stipulated ADI value for Endrin aldehyde residues in food is 0.0002 µg/g/day [44]. This ADI value is much lower than the Endrin aldehyde content of the milk samples. Also, the Endrin aldehyde content of the milk samples is much higher than the values reported by [43] for sediment (0.0005 µg/g), green algae (0.6 µg/mL), daphnid (0.74 µg/mL) and fresh water fish (1.06 µg/mL) of a riverine area of Edo state, South-south, Nigeria. Furthermore, Endrin and Endrin aldehyde were found to be 0.045 and 0.208 mg/kg, respectively in kolanuts obtained from Osun state, Nigeria [45]. The values reported in this study were much higher than the maximum values obtained for these two OCPs in the kolanut sample. Adeleye et al. [21] reported values of 0.351 and 3.491 mg/kg for Endrin and Endrin aldehyde, respectively in fluted pumpkin leaves sourced from South-western Nigeria. Endrin ketone showed levels ranging from 0.842 µg/mL in sample B to 10.020 µg/mL in sample C (the highest OCP concentration observed). It is observed to have a proportional relationship to Endrin and Endrin aldehyde. The stipulated ADI value for Endrin ketone residues in food is 0.0002 µg/g/day [44]. A study on rodents suggests that exposure to Endrin aldehyde or Endrin ketone may cause liver disease [46]. All the milk samples (A, B, C, D, E and F) contained levels of Endrin ketone exceeding the designated ADI value in food as well as the level of Endrin ketone in the gill (78.8 ng/g) and muscle (11.2 ng/g) of fish (Pomadasys commersonnil) sourced by Olisah et al. [47] from the Swartkops estuary in South Africa.

Heptachlor levels in the samples ranged between 2.750 µg/mL in Sample D and 7.832 µg/mL in sample A. Acute inhalation exposure of Heptachlor by humans has been associated with nervous system effects in a few case studies [48]. Also, gastrointestinal effects such as nausea and vomiting have been reported to occur following accidental ingestion of Heptachlor [49]. All the samples showed elevated levels of Heptachlor much higher than the ADI value (0.0001 µg/g/day) for Heptachlor in food [35] and also higher than the heptachlor residue level in maize (0.005 mg/kg) and cowpea (0.01 mg/kg) obtained from Ghana in a study carried out by Akoto et al. [50]. Heptachlor epoxide showed levels ranging from BDL in Sample A, B, C and E to 0.374 µg/mL in sample F. The ADI value for heptachlor epoxide in food is 0.000013 µg/g/day [35]. Some studies in animals suggest that young animals exposed during gestation and infancy may be very sensitive to Heptachlor and Heptachlor epoxide. Changes in nervous system and immune function were found in these animals [51]. Levels below the designated ADI values were observed for four of the samples while samples D and F had values higher than the stipulated ADI value.

Methoxychlor levels in the samples ranged between 0.950 µg/mL in Sample B to 3.414 µg/mL in Sample E. The ADI value for Methoxychlor is 0.1 µg/g/day [35]. Studies in animals show that exposure to Methoxychlor adversely affects the ovaries, uterus, and mating cycle in females, and the testes and prostate in males. Fertility is decreased in both female and male animals [52]. All the samples showed elevated levels of Methoxychlor which are much higher than the expected designated ADI value. DDD levels in the samples ranged from 0.220 µg/mL in Sample D to 4.718 µg/mL in Sample E. These concentrations are much higher than the ADI value (0.01 µg/g/day) for DDD [53]. Tests in animals also suggest that short-term exposure to DDT and metabolites in food may have a harmful effect on reproduction. In addition, products of DDT metabolism such as DDD and DDE can cause harmful effects on the adrenal gland [52]. DDE level in the samples ranged between 0.170 µg/mL in Sample B to 0.732 µg/mL in Sample C. The ADI value for DDE is 0.01 µg/g/day [53]. A study in humans showed that increasing concentrations of p,p′-DDE in human breast milk were associated with reductions in the duration of lactation. An additional study in humans found that as the DDE levels in the blood of pregnant women increased, the chances of having a pre-term baby also increased [52]. DDT levels in the samples ranged between 0.214 µg/mL in Sample F to 0.434 µg/mL in Sample C. International Agency for Research on Cancer (IARC) classified DDT as a Class 2B (possibly carcinogenic to humans) residue [34]. The ADI value for DDT is 0.01 µg/g/day [53]. People who swallowed large amounts of DDT became excitable and had tremors and seizures; they also experienced sweating, headache, nausea, vomiting, and dizziness [52]. All the samples showed elevated levels of DDD, DDE and DDT which were much higher than the expected designated ADI value. These results are comparable with the levels of DDD (0.128 mg/kg), DDE (0.053 mg/kg) and DDT (0.247 mg/kg) obtained by Olutona and Livingstone [54] in a study carried out on the OCPs content of some selected malt drinks in Nigeria where the concentration of the DDE exceeded the ADI value.

α- HCH levels in the samples ranged between 0.344 µg/mL in Sample B to 1.970 µg/mL in Sample C. The ADI value for α- HCH is 0.005 µg/g/day [55]. Long-term oral administration of α-HCH, β-HCH, γ-HCH, or technical-grade HCH to laboratory rodents has been reported to result in liver cancer [56]. β-HCH levels in the samples ranged between 0.282 µg/mL in Sample B to 1.044 µg/mL in Sample E. The ADI value for β- HCH is 0.005 µg/g/day [55]. All the samples had levels exceeding the stipulated ADI value for α-HCH andβ-HCH. γ- HCH levels in the samples ranged between 0.192 µg/mL in Sample E to 0.884 µg/mL in Sample C. The ADI value for γ-HCH is 0.005 µg/g/day [55]. In humans, breathing toxic amounts of γ-HCH and/or α-, β-, and δ-HCH can result in dizziness, headaches, and possible changes in the levels of sex hormones in the blood [56]. All the samples (except sample F) had levels exceeding the stipulated ADI value for γ- HCH.δ- HCH levels in the samples ranged between 0.436 µg/mL in sample B to 1.270 µg/mL in sample A. The ADI value for δ- HCH is 0.005 µg/g/day [55]. All the samples had levels exceeding the stipulated ADI value. These results are similar to the concentrations of α-HCH (0.10–3.10 µg/g), β-HCH (0.32–1.87 µg/g), γ-HCH(0.30–1.3 µg/g) and δ- HCH (0.06–3.37 µg/g) detected by Oyekunle et al. [9] in cocoa beans obtained from Ondo State, South-western Nigeria, based on the fact that they are all greater than their respective ADI values. The concentrations of the OCPs were above the respective European Union set maximum residue limits (EU MRLs) for different classes of OCPs. The presence of these pesticides in these evaporated milk samples is an indication that farmers in Nigeria still use these pesticides for crop production despite their prohibition. These crops are capable of contaminating the udder of cows as well as their water and feed during open grazing. Coupled with this, unsafe and careless farming practice could as well lead to direct contamination of the milk samples with the OCPs while milking. The results obtained in this study are consistent with the values earlier reported for OCPs in various samples where the OCP contents are greater than the EU/MRLs standards. For instance, Adeleye et al. [21] reported that the OCPs in amaranths and fluted pumpkin obtained in South-western Nigeria exceeded the EU MRLs. In the same vein, Olutona and Livingstone [54] reported that the OCPs (except γ- HCH) content of five different malt drinks are greater than the EU MRLs. Similar trend was observed by Akan et al. [36] when the OCPs contents of spinach, lettuce, cabbage, onions and tomatoes were compared to that of EU MRLs.

The non-carcinogenic health risks of the OCPs in the evaporated milk samples for adults, as seen in Table 3, revealed that Aldrin, Dieldrin, Endrin, Endrin aldehyde, Endrin ketone, Heptachlor and all the HCHs have HRI > 1 in sample A. Similar trend was observed in sample B (except for β-HCH and γ-HCH having HRI < 1) and C. In sample D, Aldrin, Dieldrin, Endosulfan I, Endrin aldehyde, Endrin ketone, Heptachlor, Heptachlor epoxide and all the HCH have HRI > 1. Except for Endrin and Heptachlor epoxide, sample E showed a similar trend to D. Aldrin, Dieldrin, Endrin aldehyde, Endrin ketone, Heptachlor, Heptachlor epoxide and the HCH OCPs had HRI > 1 in sample F. Consequently, it can be inferred that in all the milk samples, Aldrin, Dieldrin, Endrin aldehyde, Endrin ketone and Heptachlor had HRI > 1 which implies that the adult consumers of these evaporated milk samples might be prone to long-term potential non-carcinogenic health risk from these OCPs. However, all the milk samples showed no potential non-carcinogenic health risk in adults with respect to Endosulfan sulphate, Methoxychlor, p,p′-DDD, p,p′-DDE and p,p′-DDT.

Table 3 Potential non-carcinogenic health risk for adults
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In children, the milk samples showed potential non-carcinogenic health risk with respect to Aldin, Dieldrin, Endrin aldehyde, Endrin ketone and Heptachlor. No potential non-carcinogenic health risk was obtained for children with respect to Methoxychlor, p,p′-DDE and p,p′-DDT. This results (as seen on Table 4) is similar to the values reported by Adeleye et al. [21] for fluted pumpkin where Aldrin, Dieldrin, Endrin aldehyde and Heptachlor were found to equally have HRI values > 1 in the children category. The highest non-carcinogenic health risk index for children (490.32) was obtained from Dieldrin found in sample F while the lowest (0.03885) was found in p,p′-DDT obtained from sample B.

Table 4 Potential non-carcinogenic health risk index for children
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As seen in Table 5, all the samples showed carcinogenic potencies in adult consumers with respect to Aldrin, Dieldrin, Heptachlor, α-HCH, β-HCH and δ-HCH. Also, they all showed no carcinogenic potency with respect to DDE and DDT. The highest carcinogenic potency value was observed for sample E as 246.667 (Dieldrin) while the lowest was obtained in sample D as 0.142 (DDD). In children, the milk samples showed potential carcinogenic health risk in terms of Aldrin, Dieldrin, Heptachlor, p,p′-DDD, p,p′-DDE and the HCHs while none of the samples showed no carcinogenic potency in terms of any of the OCPs as seen in Table 6. Just like what obtains in the non-carcinogenic health risk assessment, the highest carcinogenic potency in children (4617.816) was obtained from Dieldrin in sample F while the lowest (0.776) was detected in p,p′-DDT from sample B. This result implies that children are at greater risk of carcinogenic exposure from the consumption of these milk samples compared to adults. Hence, need to control the rate of consumption by children. Furthermore, samples F and B having very high and low cumulative health risk indices, respectively confirmed the respective high cumulative OCPs load in both samples (as seen in Table 1) and this further suggests that the continuous consumption of these milk samples could put consumers at greater risk of both carcinogenic and non-carcinogenic health risks compared to other milk samples. Precisely, the risk of exposure to cancer from the consumption of these products is about four times higher than the set benchmark HRI (HRI = 1) by the European Commission Regulation (EC) in 1999 [33].

Table 5 Potential carcinogenic health risk for adults
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Table 6 Potential carcinogenic health risk for children
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The correlation coefficients of the OCPs in Table 7 indicated that out of 153 possible pairs of different congeners, 17 pairs (11.1%) were very strongly positively correlated, 18 pairs (11.8%) were moderately positively correlated while 60 (39.2%) were weakly positively correlated. Also, 2 pairs (1.3%) were strongly negatively correlated, 9 pairs (5.9%) were moderately negatively correlated while 47 (30.7) were weakly negatively correlated. It could therefore be inferred that OCPs in the evaporated milk drinks were contributed by different factors. The r value of 0.80 obtained from α-HCH and γ-HCH pair suggests that both OCP residues are basically from the same source. The same deductions can also be made for the γ-HCH & p,p′-DDE (r = 0.91) and endrin ketone and p,p′-DDE (r = 0.91) pairs.

Table 7 Correlation coefficients of the OCPs in the milk samples
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4 Conclusion

In this study, varying concentrations of OCPs were observed in the evaporated milk samples with the highest OCP load was detected in sample E. The study concluded that the highest estimated cumulative carcinogenic and non-carcinogenic potencies of the OCPs in children were found in samples F and C, respectively, and this could lead to serious health issues with constant consumption of these milk samples. In adults, the highest cumulative non-carcinogenic and carcinogenic health risks were found to come from sample C. Considering the consumption rate of these products in Nigeria, the regular consumption of these products (especially sample C) could possibly pose a long term non-carcinogenic and carcinogenic health risks to regular consumers due to the possible accumulation of the studied OCPs in the body.