Investigating DDT presence in vegetables, fish and human breast milk using analytical chemistry techniques in the Green Mountain area of East Libya

Abstract

The toxicity of p,p′-dichlorodiphenyltrichloroethane (DDT) led to a ban on its use ever since the late 1970s. However, its long half-life makes it a persistent environmental pollutant that is found ubiquitously in various matrices and has transferred into the food chain consequently it is possible to find DDT and its residues in humans. Initial studies had shown the presence of DDT in vegetables grown in the Gebel Akhdar region of Eastern Libya. Given this, investigations were undertaken for the presence of DDT and its metabolites (p,p′-DDT, o,p′-DDT, p,p′-DDE, o,p′-DDE, p,p′-DDD and o,p′-DDD) in different biological matrices including human breast milk, human colostrum and human blood from people in Eastern Libya as well as food matrices from fish, vegetables which form part of a typical diet of inhabitants of the region. All extraction techniques were performed using modified QuEChERS procedures with a Dispersive Solid Phase Extraction (d-SPE) C18 with extraction efficiencies ranging between 86 and 103%. The extraction was followed by Gas chromatography-mass spectrometry (GCMS) using a single ion mode to identify and quantify residue levels of the pesticide and its metabolites. Human breast milk (50 samples) and colostrum (20 samples) from different locations in Eastern Libya were analysed for DDT and its metabolites. The predominant compounds found in order of prevalence, p,p′-DDE, o,p′-DDE followed by p,p′-DDT, p,p′ DDD, o,p′-DDT and o,p′ DDD. The value of the sum of the means of DDTs (∑DDTs) found was 1.712 mg/kg lipid weight (lw). The highest values of DDTs were found to be from rural locations. The results indicate a strong correlation between concentrations of p,p′-DDE and p,p′-DDT with lower birth weights, age of mothers and weekly fish intake. The metabolites p,p′-DDD and p,p′-DDE showed a strong correlation with the number of miscarriages (99% accuracy). Some 30% of contaminated samples were higher than the maximum residual level (MRL is 0.05 mg/Kg Lw) permitted by WHO. The estimated daily intake (EDI) of DDTs pesticide was found to be higher than the TDI (tolerable daily intake) in rural areas of 20 g/kg bw/day. The analysis of colostrum indicated that 4 of the 10 samples from El-Marj city contained p,p′-DDE with a mean concentration 0.1 ± 0.07 mg/kg Lw. Whilst only 20% of Benghazi’s colostrum samples were contaminated with p,p′-DDE (0.16 ± 0.001 mg/kg Lw). There was a positive correlation between the concentration of p,p′-DDE in colostrum and the age of mothers with a Spearman’s value of 0.79 and p-value approximately zero. The presence of DDT and its metabolites and their possible association with cancer risk, blood serum samples were collected from 52 breast and colon cancer patients and control subjects at (Benghazi Medical Centre, Department of Oncology). DDT concentrations were determined in 39 cases in those with a diagnosis of cancer and in 13 cases of the control subjects. The metabolite p,p′-DDE was present in 97.4% of all cancer patients but only in 53.8% of the control patients. In all the samples, p,p′-DDE was found in 86.5% of the blood serums, whereas o,p′- DDE was found only in 38.5%. and p,p′-DDT was in 28.8% and the lowest quantity of metabolite found was of p,p′-DDD in 17.3% of samples. DDT and DDD were found in low concentrations ranging from 0.00-0.001×10-3 mg/kg Lw. Mean values of p,p′-DDE concentrations were 3.5 ± 4 ×10–3 mg/kg (with range 0.00-20 ×10–3 mg/kg) in breast cancer patients and 1.49±2 ×10–3 mg/kg (range 0.00-6.0 ×10–3 mg/kg) in the colon cancer patients. In contrast, the control group had a mean of p,p′-DDE of 0.82±1 ×10–3 mg/kg (range 0.0-5.0 ×10–3 mg/kg). A significant correlation was found between total ∑DDTs metabolites levels and location. There was a significant association found between the concentration of DDE and the presence of breast and colon cancer. Other significant correlations between DDE levels and factors such as age and gender were found. The longer the lactation period and the greater the number of births of mothers was negatively correlated with DDE levels. The human health risk associated with dietary exposure to DDTs and its metabolites through the consumption of fish species was investigated by analysing for the pollutants in species (Mullus barbatus, Galeorhinus, Pagellus, Epinephelus, Sardinella aurita and Salmon). DDTs concentration ranged between 0.0001 and 0.009 mg/kg ww (mean 0.0044 mg/kg ww with 0.006 standard deviation or 0.080 mg/kg Lw). 71% of all fish samples showed the presence of DDT and its metabolites however levels did not exceed MRL. The estimated daily intake EDI and hazard ratio HQ Levels were calculated for adults and children to assess the potential cancer risks associated with these DDT contaminants due to fish consumption in the human diet. Mullus barbatus and Salmon, showed a significant cancer risk at the 95th Percentile intake for adults, have a similar cancer of 1.1×10-2 . The consumption of these should not exceed seven meals per month. The cancer risk from other fish was two orders of magnitude lower. Residual DDT and its metabolites were investigated in 290 of domestically grown and imported vegetable samples (cucumber, zucchini, onion, eggplant, lettuce, and Arugula or Rucola) Contamination by p,p′-DDE was found in 76.92% of the samples with concentrations ranging from 0.0009 to 0.0052 mg/kg ww. Its isomer o,p′-DDE contaminated 42% of samples with concentration levels between 0.0009 and 0.005 mg/kg ww. The metabolite p,p′-DDD was found in 20% of samples at levels of 0.002 mg/kg ww. Cancer risk from consumption of domestic cucumbers ranged between (1.4×10-3 to 6.4 ×10-4 ) and for imported cucumbers were found between (1.3×10–5 to 6.4×10-–4 ) and imported onions ranged from 1.2×10–4 to 8.2×10–4 which suggests that in some locations, both these vegetables exceeded the standard cancer risk of 1×10-6 . The presence of DDT and its metabolites in commonly consumed foodstuffs in the markets of Eastern Libya have been shown to pose significant cancer risks. There are also some risks associated with human milk consumption by infants as the pesticide and its metabolites are also found in breast milk samples collected from mothers in the region. This coupled with correlations between the pollutants and both colon and breast cancer suggest that monitoring pesticide residues in diverse crops and the environment should be expanded to improve consumer health protection.