Risk of DDT residue in maize consumed by infants as complementary diet in southwest Ethiopia

Apparent Khat chewers exposure to DDT in Ethiopia and its potential toxic effects: A scoping review

Dichlorodiphenyltrichloroethane (DDT) is an insecticide, a member of dirty dozen persistent organic pollutants, used widely in the world until it was banned in the 1970s.The banning of DDT was strengthened by the Stockholm Convention in 2001. DDT is allowed only for malaria control in Ethiopia. However, farmers are misusing DDT and applying it to Khat (Catha edulis) farming. So, this review analyzes available data in the literature on the current trend, application, occurrence, fate and effects of DDT and its metabolites, dichlorodiphenyldichloroethane (DDD), dichlorodiphenyldichloroethylene (DDE), in the chewable parts of Khat. Generally, the concentration level of DDT, DDD, and DDE, designated as DDTs, is detected in different farmlands of Ethiopia. Some of the DDTs concentrations detected are very high (141.2-973 μg/kg (Gelemso), 194.4-999 μg/kg (Aseno) and 6253-8413.3 μg/kg (Gurage), and these concentrations may indicate increasing recent unmonitored application of DDT on Khat leaves. Some of the detected concentrations of DDT in the literature were above the maximum residue limit (MRL) set by FAO/WHO (100 μg/kg) and the European Commission 10 μg/kg in vegetables and 50 μg/kg in cereals. DDT exposure of Khat chewers linked to the concentration of DDT on Khat leaves and the amount of Khat consumed. DDT might pose health risks to chewers due to chronic toxicity, bioaccumulation, persistent and endocrine disruption properties.

Recombinant expression and characterization of GSTd3 from a resistant population of Anopheles arabiensis and comparison of DDTase activity with GSTe2

The development of insecticide resistance in malaria vectors is a challenge for the global effort to control and eradicate malaria. Glutathione S-transferases (GSTs) are multifunctional enzymes involved in the detoxification of many classes of insecticides. For mosquitoes, it is known that overexpression of an epsilon GST, GSTe2, confers resistance towards DDT and pyrethroids. In addition to GSTe2, consistent overexpression of a delta class GST, GSTd3, has been observed in insecticide resistant populations of different malaria vector species. However, the functional role of GSTd3 towards DDT resistance has not yet been investigated. Here, we recombinantly expressed both GSTe2 and GSTd3 from Anopheles arabiensis and compared their metabolic activities against DDT. Both AaGSTd3 and AaGSTe2 exhibited CDNB-conjugating and glutathione peroxidase activity and DDT metabolism was observed for both GSTs. However, the DDT dehydrochlorinase activity exhibited by AaGSTe2 was much higher than for AaGSTd3, and AaGSTe2 was also able to eliminate DDE although the metabolite could not be identified. Molecular modeling revealed subtle differences in the binding pocket of both enzymes and a better fit of DDT within the H-site of AaGSTe2. The overexpression but much lower DDT metabolic activity of AaGSTd3, might suggest that AaGSTd3 sequesters DDT. These findings highlight the complexity of insecticide resistance in the major malaria vectors and the difficulties associated with control of the vectors using DDT, which is still used for indoor residual spraying.

Identification and Risk Assessment of Priority Control Organic Pollutants in Groundwater in the Junggar Basin in Xinjiang, P.R. China

The Junggar Basin in Xinjiang is located in the hinterland of Eurasia, where the groundwater is a significant resource and has important ecological functions. The introduction of harmful organic pollutants into groundwater from increasing human activities and rapid socioeconomic development may lead to groundwater pollution at various levels. Therefore, to develop an effective regulatory framework, establishing a list of priority control organic pollutants (PCOPs) is in urgent need. In this study, a method of ranking the priority of pollutants based on their prevalence (Pv), occurrence (O) and persistent bioaccumulative toxicity (PBT) has been developed. PvOPBT in the environment was applied in the screening of PCOPs among 34 organic pollutants and the risk assessment of screened PCOPs in groundwater in the Junggar Basin. The results show that the PCOPs in groundwater were benzo[a]pyrene, 1,2-dichloroethane, trichloromethane and DDT. Among the pollutants, benzo[a]pyrene, 1,2-dichloroethane and DDT showed high potential ecological risk, whilst trichloromethane represented low potential ecological risk. With the exception of benzo[a]pyrene, which had high potential health risks, the other screened PCOPs had low potential health risks. Unlike the scatter distribution of groundwater benzo[a]pyrene, the 1,2-dichloroethane and trichloromethane in groundwater were mainly concentrated in the central part of the southern margin and the northern margin of the Junggar Basin, while the DDT in groundwater was only distributed in Jinghe County (in the southwest) and Beitun City (in the north). Industrial and agricultural activities were the main controlling factors that affected the distribution of PCOPs.

Occupational and environmental pesticide exposure and associated health risks among pesticide applicators and non-applicator residents in rural Ethiopia

Intensive pesticide use increased concern about the potential acute and chronic health effects of pesticides in general and among applicators in particular. This study aims to explore occupational and environmental pesticide exposure and health risks among pesticide applicators and residents. A community-based cross-sectional study was conducted involving 1,073 individuals. We examined the health effects potentially attributable to pesticide exposure using regression to estimate prevalence ratios (PR). A higher proportion of good knowledge of pesticides [75 vs. 14%; APR = 1.542 (1.358-1.752), p < 0.001] and a higher mean score of perceived health risk of pesticide use [4.21 vs. 3.90; APR = 1.079 (1.004-1.159), p < 0.05] were observed among applicators than residents. A significantly higher proportion of applicators experienced health effects presumably related to pesticide exposure among themselves (36%) than residents (16%), and a higher proportion of them used prescribed drugs in the past 12 months [51 vs. 32%; APR = 1.140 (1.003-1.295), p < 0.05]. Skin irritation, shortness of breath, cough, and dizziness were more likely reported by applicators than residents. Perceived toxicity of currently applied pesticide products, mix pesticides without gloves, regularly maintain and wash sprayer tank after application, occurrence of an incidental splash during mixing and application, and using home-based care after experiencing a symptom presumably due to pesticide exposure were significantly associated with health effects among applicators. Use of face mask and visiting health facility when experiencing a symptom presumably due to pesticide exposure were significantly positively correlated with attending training on the health risks and use of pesticides. A substantial proportion of applicators reported improper use of preventive measures and methods of pesticide waste disposal. These observations point out that applicators can face high health risks of occupational pesticide exposure in Ethiopia. Even trained applicators pursued poor preventive practices; hence, comprehensive practice-oriented in-depth training focusing on safety precautions and proper use of personal protective equipment, and provision of adequate pesticide waste disposal means are crucial interventions.

Exposure of infants to organochlorine pesticides from breast milk consumption in southwestern Ethiopia

Breast milk is often used as an environmental bioindicator since it serves as an important medium to accumulate organochlorine pesticides. The main aim of this study is to determine the level of organochlorine pesticides in human breast milk collected from three districts of southwestern Ethiopia (Asendabo, Deneba, and Serbo) at three times points baselines (1st month), midline ( six months), and end line (12 months) and risk of infants’ exposure. A longitudinal study was conducted to assess pesticide residues in human breast milk samples and evaluate the risk-exposure of infants to these pesticides from consumption of mother’s milk in Ethiopia. Breast milk samples were collected from 168 mothers at three time points and pesticides were extracted using the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. The level of pesticide residues in human milk samples and exposure of infants to the pesticides was evaluated by calculating the estimated daily intake and compared with the provisional tolerable daily intake of the pesticides under study. The results indicated that, from the eight organochlorine pesticides analyzed in 447 breast milk samples at three sampling times, DDT and its metabolites were detected. p,p′-DDE and p,p′-DDT were detected in all (100%) of the breast milk samples while, p,p-DDD, and o,p-DDT were detected in 53.9%, and 42.7%, respectively. The mean concentration of total DDT at three time points(baseline, midline and endline) were 2.25, 1.68 and 1.32 µg/g milk fat, respectively. The mean concentration of total DDT from the three districts was 1.85 µg/g milk fat which is above the maximum residue limit (MRL = 0.02 µg/g milk fat set by FAO/WHO). The mean ratio of DDT/DDE for the three areas was calculated less than five (< 5) indicates historical DDT use in the study area. The estimated daily intake of infants at the first month of breastfeeding was 11.24 µg/kg-BW/day, above the provisional tolerable daily intake (PTDI) for total DDT set by FAO/WHO, which is 10 µg/kg body weight. An intake of OCPs is a big concern for infants' health in Ethiopia and countries with a similar condition, particularly at the first month of lactation. Strict regulations of the health-threatening pesticide by the regulatory body (Environment, Forest and Climate Change Commission) at the country and regional levels is advocated.

Pesticide Use, Perceived Health Risks and Management in Ethiopia and in Hungary: A Comparative Analysis

Pesticides play a very important role for ensuring food security and economic growth but their use can cause harmful effects to human health and to the environment. The study aimed to investigate the level of knowledge, health risk perceptions, and experiences on the practice of pesticide use and management among extension officers in Ethiopia and plant doctors in Hungary. A questionnaire survey among 326 officers was conducted in the two study areas and data were analyzed by ordinal logistic regression. According to the findings, Hungarian officers had much better knowledge of pesticide products (92%), and less frequently experienced pesticide poisoning among applicators (7%) than the Ethiopians (66% and 41%, respectively). Hungarian officers perceived less health risk of pesticide use (AOR = 0.46, 95%, Cl: 0.27-0.80), were ten times more likely to deem the pesticide management system effective (AOR = 10.23, 95%, Cl: 5.68-18.46) and were nine times more likely to report that applicators used personal protective equipment (AOR = 8.95, 95%, Cl: 4.94-16.28). A significant proportion of officers from both countries reported inappropriate methods of pesticide residue disposal. These observations point out that the situation of pesticide use and knowledge and management of pesticide products is definitely better in Hungary; nevertheless, the issue continues to need more attention in both settings.

Exposure to organochlorine pesticides as a predictor to breast cancer: A case-control study among Ethiopian women

Breast cancer (BC) is becoming one of the most prevalent non-infectious disease in low and middle income countries. The steady rise of BC incidence may be related to the different risk factors. Among many, rampant presence of environmental pollutants might be one of the risk factors. Therefore, the aim of this study is to investigate exposure to organochlorine pesticides as a risk factor to breast cancer. A case-control study design was employed among breast cancer patients and non-breast cancer individuals (controls). Blood samples were collected from 100 study participants (50 cases and 50 controls) followed by serum separation, extraction and cleanup using standard analytical procdures. The findings revealed that ten organochlorine pesticides were detected in the serum of the study participants. From the detected organochlorine pesticides, heptachlor was observed at higher concentration for breast cancer patients (6.90±4.37 μg/L) and controls (9.15±3.84 μg/L). Mean serum level of p,p’-DDE, p,p’-DDT, heptachlor, gamma-chlordane, endosulfan, and dibutyl-chlorendate were significantly higher in the serum of breast cancer patients than the controls. From the studied pesticides, p,p’-DDT and gamma-chlordane are significant predictors for BC, while, others are equivocal. A unit increment of the concentration of p,p’-DDT (AOR; 2.03, 95% CI: 1.041–3.969) increased the odds of developing breast cancer by two, while for gamma-chlordane (AOR;3.12, 95% CI; 1.186–8.203) by three. Our study results suggesting that, organochlorines are a risk factors for breast cancer in Ethiopia. Decreasing exposure to such organochlorines might have a significant public health relevance in reducing non-communicable chronic illnesses. Besides, continues monitoring of persistent organic pollutants using body biomarkers is important for disease prevention and device mitigation measures.

Risk of dietary intake of organochlorine pesticides among the childbearing-age women: A multiple follow-up study in North China

Exposure to organochlorine pesticides (OCPs) can cause adverse health effects in the female population. We investigated the dietary OCP intake of childbearing-age women living in large agricultural areas of Northern China, as well as their associated health risks. Ten childbearing-age women were recruited during 2015-2016. Their weekly dietary intake diaries and food samples were collected over the course of five visits. The OCP residues of 322 food samples from seven categories (i.e., cereal, vegetable, fruit, fish, meat, egg, and milk) were analyzed by gas chromatography-mass spectrometry. The average concentrations of the total hexachlorocyclohexanes (ΣHCH), dichlorodiphenyltrichloroethanes and their metabolites (ΣDDX), endosulfans (ΣES), and dieldrin and endrin (ΣDrin) in all food categories were, overall, much lower than the maximum residue limits. Relative high mean residues of ΣDrin and ΣES were found in fruits (ΣDrin: 0.687 ng g-1 wet weight (w.w.), ΣES: 2.24 ng g-1 w.w.) and vegetables (ΣDrin: 0.690 ng g-1 w.w., ΣES: 2.11 ng g-1 w.w.). The estimated daily dietary intake (EDI) of these compounds was calculated, with mean levels of 10.6 (ΣES) > 4.37 (ΣDrin) > 1.51 (ΣHCH) > 0.850 (ΣDDX) ng kg-1 day-1. Women during the heating period (from January to March) tended to ingest more ΣHCH, ΣDDX, ΣDrin, and ΣES. Overall, women had no obvious non-carcinogenic and carcinogenic risks due to intake of OCPs, but 83.9% of them has potential carcinogenic risk, with estimated life carcinogenic risk (LCR) exceeding 10-6. Furthermore, women had a higher potential carcinogenic risk during the heating period (mean LCR: 1.33 × 10-5) than during the non-heating period (mean LCR: 8.50 × 10-6). ΣDrin was the dominant OCP responsible for health risks, followed by ΣHCH. We concluded that women in North China still have some dietary OCP intake, especially during the heating period.

Environmental and Health Risks of Pesticide Use in Ethiopia

BACKGROUND

There are frequent reports of unsafe pesticide use in many parts of Africa. Ethiopia is the second most populous nation in Africa with around 80% of the population still depending on agriculture which intensively uses pesticides. A number of studies have examined pesticide-related health and environmental risks in Ethiopia. However, most of these studies have been small in scale and it is therefore challenging to get a general overview of the extent of health risks and level of environmental contamination in the country.

OBJECTIVES

The aim of the present study was to synthesize and summarize contemporary knowledge on pesticide-related risks and relevant gaps in Ethiopia.

METHODS

An electronic database search and gathering of grey literature were done to collect information on the risks of pesticide use in Ethiopia. The electronic search was conducted using MEDLINE (via PubMed) without any publication date or language specifications. The Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) checklist was used as guide in the creation of this review.

DISCUSSION

A synthesis of the reviewed studies showed evidence of health risks due to occupational pesticide exposure, surface water pollution with pesticides that could cause chronic health risks to the public, evidence of pesticide contamination of the environment (e.g., soil organisms, fish, bee colonies and wildlife) and local as well as international consumer risks due to pesticide residues in food items. In addition, there have been frequent reports of health and environmental hazards in association with cut-flower farms. There is also evidence of direct use of DDT (dichlorodiphenyltrichloroethane) on food crops and detection of DDT residues in surface water, soil and human breast milk. Those reported risks might be due to lack of knowledge among farm workers, negligence of farm owners, absence of post-registration monitoring systems and poor implementation of both national and international regulations in Ethiopia due to poor institutional capacity.

CONCLUSIONS

The health and environmental risks of inappropriate use of pesticides requires action by all concerned bodies. Improved institutional arrangements for enforcement of regulations, awareness and further intervention studies could lessen the high risks of pesticide misuse.

COMPETING INTERESTS

The authors declare no competing financial interests.

Contamination of Foods from Cameroon with Residues of 20 Halogenated Pesticides, and Health Risk of Adult Human Dietary Exposure

(1) Background: Halogenated pesticides are abundantly used in Cameroon, but there is no information on the health risk of consumers from exposure to their residues in foods. (2) Methods: Residues of 20 halogenated pesticides were determined in 11 agricultural products collected in the 3 largest cities of Cameroon using QuEChERS extraction and gas chromatography with electron capture detector (GC-ECD), and health risk from dietary exposure was assessed. (3) Results: Organochlorines pesticides aldrin, p,p'-dichlorodiphenyl-trichloroethane (DDT) and β-hexachlorocyclohexane (β-HCH) found in 85.0%, 81.9% and 72.5% of samples, respectively, were the most frequently detected. The highest average concentrations of residues were 1.12, 0.74 and 0.39 mg/kg for methoxychlor, alachlor and β-HCH, respectively, found in chilli pepper. Chili pepper (58.9%), cowpea (56.8%), black beans (56.5%) and kidney beans (54.0%) exhibited the highest residue occurrences. Levels above the European Union maximum residue limits (MRLs) were found for all the 20 pesticides, in 40.1% of the positive analyses, and the food samples contained 14 pesticides banned in Cameroon. Chronic, acute, cumulative and carcinogenic risk assessments revealed that lifetime consumption of maize, black beans, kidney beans, groundnuts and chili pepper contaminated with aldrin, dieldrin, endrin, HCB, heptachlor, o,p'-DDT, p,p'-DDD, p,p'-DDT, p,p'-DDE and β-HCH, could pose health risks. (4) Conclusion: These results show that there is an urgent need of pesticide usage regulation, effective application of pesticide bans and management of obsolete pesticide stocks in Cameroon.

Pesticide traces in local crops of Sancti Spíritus, Cuba: risk assessment study

Background

Vegetables and rice produced in Cuba may contain residue of pesticides that exceed the maximum residue limits (MRLs). Pesticide residues on crop samples from Sancti Spíritus province were analyzed. Based on these residue data, a risk assessment of consumer exposure was conducted.

Methods

Samples collected during the 2017, 2018, and 2019 periods were analyzed using UPLC-MS/MS and GC/ECD chromatography techniques. A deterministic risk assessment was performed, using consumption data collected by the authors. Also, a probabilistic risk assessment was worked out with @RISK for the Monte Carlo simulation.

Results

A broad range of pesticides were detected in the samples. Most of the detected active ingredients were insecticides and fungicides. A considerable part of the detected pesticide residues exceeded the EU and Cuban MRLs. However, the deterministic risk assessment revealed that the consumer risk of pesticide exposure is low. Only in the maximum exposure scenario children and adults were exposed to methamidophos residues in tomatoes higher than the acceptable daily intake.

Conclusions

When a more realistic consumption (50th percentile) and higher (95th percentile) consumption pattern for tomatoes was assumed, the deterministic risk assessment found no chronic risk for children and adults being exposed to methamidophos present in the tomato samples. Furthermore, the probabilistic risk assessment concerning methamidophos exposure in tomato for children and adult strata showed no risk. To perform in the future a more accurate risk assessment for Cuban consumers it is important to have more detailed consumption data and an expanded dataset of the residues in different crops.

Dietary risk assessment of organochlorine pesticide residues in maize-based complementary breakfast food products in Nigeria

The study assessed the levels of organochlorine pesticides (OCPs) in eight brands (A-H) of regularly consumed maize-based complementary/breakfast foods in Nigeria. We also evaluated the dietary exposure of infants and young children to the detected OCPs. The OCP residues were quantified using GC-ECD. A total of 10 OCPs residues (β-HCH, δ- HCH, heptachlor, endosulfan sulfate, aldrin, endrin, dieldrin, p,p’-DDE, p,p’-DDT and methoxychlor) were detected. Total OCPs burden was highest in brands F, D, and G with mean concentrations of 45.98 mg kg⁻¹, 28.54 mg kg⁻¹ and 21.87 mg kg⁻¹, respectively and the lowest burdens in brands H (1.72 mg kg⁻¹) and A (6.61 mg kg⁻¹). Hazard index (HI) for all the age categories were >1 and all the 6 carcinogens (β-HCH, heptachlor, aldrin, dieldrin, p,p’-DDE, and p,p’-DDT) identified had cancer risk index range of 5.43 × 10⁻⁴ to 2.05 × 10⁻⁶ which were above acceptable risk. These results indicated the possibility of both systemic and cancer risks to infants and children consumers of the foods. Food brands manufacturers need to carry out regular pesticide residues analysis of raw materials especially maize prior to the production in order to ensure food safety and quality.

Gap analysis of nickel bioaccessibility and bioavailability in different food matrices and its impact on the nickel exposure assessment

The metal nickel is well known to cause nickel allergy in sensitive humans by prolonged dermal contact to materials releasing (high) amounts of nickel. Oral nickel exposure via water and food intake is of potential concern. Nickel is essential to plants and animals and can be naturally found in food products or contamination may occur across the agro-food chain. This gap analysis is an evaluation of nickel as a potential food safety hazard causing a risk for human health. In the first step, the available data regarding the occurrence of nickel and its contamination in food and drinks have been collected through literature review. Subsequently, a discussion is held on the potential risks associated with this contamination. Elevated nickel concentrations were mostly found in plant-based foods, e.g. legumes and nuts in which nickel of natural origin is expected. However, it was observed that dedicated and systematic screening of foodstuffs for the presence of nickel is currently still lacking. In a next step, published studies on exposure of humans to nickel via foods and drinks were critically evaluated. Not including bioaccessibility and/or bioavailability of the metal may lead to an overestimation of the exposure of the body to nickel via food and drinks. This overestimation may be problematic when the measured nickel level in foods is high and bioaccessibility and/or bioavailability of nickel in these products is low. Therefore, this paper analyzes the outcomes of the existing dietary intake and bioaccessibility/bioavailability studies conducted for nickel. Besides, the available gaps in nickel bioaccessibility and/or bioavailability studies have been clarified in this paper. The reported bioaccessibility and bioavailability percentages for different food and drinks were found to vary between <LOD and 83% and between 0 and 30% respectively. This indicates that of the total nickel contained in the foodstuffs only a fraction can be absorbed by the intestinal epithelium cells. This paper provides a unique critical overview on nickel in the human diet starting from factors affecting its occurrence in food until its absorption by the body.

Reduction of pesticide residues from teff (Eragrostis tef) flour spiked with selected pesticides using household food processing steps

Teff (Eragrostis tef) is an ancient cereal that is indigenous from Ethiopia. Nowadays, teff grain is becoming popular to many parts of the world. Teff is gluten-free in nature, has high iron and fiber content, and many other health benefits make this crop interesting to many consumers. Since no insect pests are attacking the teff grains, farmers do not apply pesticides on it, unlike maize and other grains. Nevertheless, residues of organochlorine pesticides have been detected at an alarming level that could pose a consumer risk. Teff is often consumed as injera which is a fermented flat pancake. The main aim of the present study is, therefore, to investigate the effect of household food processing (doughing and baking) on the reduction of pesticide residues from teff. Pesticide residues previously detected in teff grain such as permethrin, cypermethrin, deltamethrin, chlorpyrifos ethyl, p,p'-DDE, p,p'-DDD, o,p'-DDT, and p,p'-DDT were spiked and extracted followed by the subsequent household processing which are generally doughing (dough making followed by fermentation) and baking. From the findings of this study, doughing decrease the pesticide residues in the range of 59.9-86.4% and baking in the range of 63.2-90.2%. Kruskal-Wallis analysis indicates that the reduction of pesticide residues by baking is significantly different from doughing (p-value < 0.0001). There is also a significant difference between non-fermented and fermented dough (p-value = 0.012). The processing factor for doughing and baking was less than one (PF < 1 = reduction factor) which indicates the reduction of pesticides due to teff processing. The cumulative effect of these processing methods is important to evaluate the risks associated with the ingestion of pesticides, particularly in teff grain.

Risk assessment of the endocrine-disrupting effects of nine chiral pesticides

The increased release of chiral pesticides into the environment has generated interest in the role of enantioselectivity in the environmental fate and ecotoxicological effects of these compounds. However, the information on the endocrine disrupting effects (EDEs) of chiral pesticides is still limited and discrepancies are also usually observed among different assays. In this study, we investigated the enantioselectivity of EDEs via estrogen and thyroid hormone receptors for nine chiral pesticides using in vitro and in silico approaches. The results of the luciferase reporter gene assays showed 7 chiral pesticides possessed enantioselective estrogenic activities and 2 chiral pesticides exerted thyroid hormone antagonistic effects. Proliferation assays in MCF-7 and GH3 cells were also used to verify the results of the dual-luciferase reporter gene assays. At last, the molecular docking results indicated that the enantioselective EDEs of chiral pesticides were partially due to enantiospecific binding affinities with receptors. Our data not only show enantioselective EDEs of nine chiral pesticides, but also would be helpful to better understanding the molecular biological mechanisms of enantioselectivity in EDEs of chiral pesticides.

Exposure to DDT and its metabolites from khat (Catha edulis) chewing: Consumers risk assessment from southwestern Ethiopia

Khat (Catha edulis) is one of the most consumed plant in the horn of African countries. However, it is a stimulant plant that has several side effects on the health of consumers. On top of that, the khat leaves used for human consumption are often contain contaminants such as pesticide residues. The present study aims to investigate the level of DDT residue and its metabolites (p'p-DDE, p'p-DDD, o'p-DDT and p'p-DDT) in khat samples and to undertake exposure assessment to consumers. The khat samples were collected from local markets in southwestern Ethiopia. Consumption survey was undertaken using 24 h recall method for both male and female khat consumers. The finding showed that 80% of the khat samples contained DDT and its metabolites. Some of the residues were above the maximum residue limit (MRL) set by Food and Agricultural Organization (FAO). The concentration of p'p-DDE and p'p-DDT in khat were in the range of 0.033-0.113 and 0.010-0.026 mg/kg, respectively. High concentration of the metabolite (p'p-DDE) compared to the parent compound (p'p-DDT) revealed the historical use of DDT in the study area. Probabilistic exposure analysis indicated that the mean and 97.5 percentile (P97.5), of the estimated daily intake of total DDT were 0.002 and 0.006 mg/kg bw/day, respectively. The study concluded that khat consumers are exposed to the stimulant effect of the plant as well as DDT and its metabolites in Jimma zone.

Bioaccessibility of selenium after human ingestion in relation to its chemical species and compartmentalization in maize

Selenium is a micronutrient needed by all living organisms including humans, but often present in low concentration in food with possible deficiency. From another side, at higher concentrations in soils as observed in seleniferous regions of the world, and in function of its chemical species, Se can also induce (eco)toxicity. Root Se uptake was therefore studied in function of its initial form for maize (Zea mays L.), a plant widely cultivated for human and animal food over the world. Se phytotoxicity and compartmentalization were studied in different aerial plant tissues. For the first time, Se oral human bioaccessibility after ingestion was assessed for the main Se species (Se(IV) and Se(VI)) with the BARGE ex vivo test in maize seeds (consumed by humans), and in stems and leaves consumed by animals. Corn seedlings were cultivated in hydroponic conditions supplemented with 1 mg L(-1) of selenium (Se(IV), Se(VI), Control) for 4 months. Biomass, Se concentration, and bioaccessibility were measured on harvested plants. A reduction in plant biomass was observed under Se treatments compared to control, suggesting its phytotoxicity. This plant biomass reduction was higher for selenite species than selenate, and seed was the main affected compartment compared to control. Selenium compartmentalization study showed that for selenate species, a preferential accumulation was observed in leaves, whereas selenite translocation was very limited toward maize aerial parts, except in the seeds where selenite concentrations are generally high. Selenium oral bioaccessibility after ingestion fluctuated from 49 to 89 % according to the considered plant tissue and Se species. Whatever the tissue, selenate appeared as the most human bioaccessible form. A potential Se toxicity was highlighted for people living in seleniferous regions, this risk being enhanced by the high Se bioaccessibility.

Residues, spatial distribution and risk assessment of DDTs and HCHs in agricultural soil and crops from the Tibetan Plateau

Due to its high elevation and cold temperature, the Tibetan Plateau (TP) is regarded as the "Third Pole". Different from other polar regions, which are truly remote, the TP has a small population and a few agricultural activities. In this study, agricultural soil and crop samples (including highland barley and rape) were collected in the main farmland of the TP to obtain the contamination levels of dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) in the Tibetan agricultural system as well as the relevant human exposure risks. The average concentrations of DDTs and HCHs in the agricultural soil, highland barley and rape were 1.36, 0.661, 1.03 ng/g dw and 0.349, 0.0364, 0.0225 ng/g dw, respectively. In the agricultural soil, DDTs and HCHs metabolism (DDE, DDD and β-HCH) were abundant, which indicated a "historical" source, whereas crops contained a similar composition ((DDE + DDD)/DDT, α/β-HCH and α/γ-HCH) to that of wild plants, suggesting that the DDTs and HCHs in crops are likely from long range atmospheric transport. The human health risks via non-dietary and dietary to DDTs and HCHs in the farmland were assessed. All of the hazard index (HI) values of DDTs and HCHs for non-carcinogenic risks were <1, and most of the cancer risk values were <10(-6), suggesting that DDTs and HCHs in the farmland will not pose non-carcinogenic risks and will pose only very low cancer risks to the Tibetan residents.