Pesticides in Vegetables
Table 1 shows the mean residual pesticides concentration of OCPs. The total concentration of DDTs (sum of P-P’ DDT, P-P’ DDE, P-P’DDD) ranges from ND–66.6, ND–66.6, ND–20, ND–53.3, ND–50 ND–16.6 and ND–16.7 μg kg–1, HCHs (α- HCH, β-HCH, γ-HCH) from ND–133.3, ND–53.3, ND–16.6, ND–103, ND–26.6, ND–6.6 and ND–23.3 μg kg–1 and in the case of endosulphan, from ND–36.63, ND–16.2, ND–73, ND–0.3, ND–70, ND–33.3 and ND–33.3 μg kg–1 in cabbage, cauliflower, spinach, celery, lettuce, broccoli and in mustard respectively. The sum of OCPs in these crops decrease in the following order cabbage > broccoli > lettuce > cauliflower > celery > spinach > mustard. The detection frequency for HCHs and DDTs was 81% and for endosulphan it was 71% respectively. The dense, waxy, and hairy foliage of brassica in combination with the lipophilic character of pesticides offers more deposition of pesticides in these vegetables. The uptake of pesticides from roots can be influenced by many factors e.g., plant species, its growth, loss from the surface of the leaf due to transpiration, pesticides metabolism and physico-chemical characteristics of pollutants (Liu et al., 2020) (Singh et al., 1990). The application rate of pesticides also varies at different sampling points that can also influence the uptake of pesticides. Cabbage is the widely grown crop; therefore more pesticides are used by the farmers for maintaining its quality under tropical conditions (Mazlan and Mumford, 2005). The ratio of DDT/DDE and γ-HCH/α-HCH indicated that the environment in which these vegetables are grown is polluted by both the new sources of HCHs and the old sources DDT. The new sources could be dangerous for human health as well as for environment. The order of percentages of OCPs above MRL set by EU was as follows: lettuce (7.7%) > mustard (6.0%) > spinach (4.7%) > cabbage (5.7%) cauliflower (4.3%) > broccoli (3.0%). The cabbage farms are the mostly contaminated, occupying 1170 ha out of 7050 ha of total vegetables cultivated area (92%) (Mazlan and Mumford, 2005).
OPPs are effective in controlling a variety of insects on vegetable crops. The concentration of OPPs decreases in the order; cabbage > cauliflower > lettuce > broccoli > spinach > celery > mustard. It is evident from the results that all vegetables were contaminated by OPPs and cabbage seemed to be contaminated the most. The concentration of OPPs were in the range of ND–233.3, ND–200, ND–10, ND–200, ND–200, ND–166.7 and ND–27.7 μg kg–1 in cabbage, cauliflower, celery, spinach, broccoli,, lettuce and mustard respectively. Among OPPs, dimethoate was found abundantly and the sum of its average mean concentration in all vegetable samples was 149.6 μg kg–1. Cabbage was found to be the most contaminated followed by cauliflower as its head and leaves were badly damaged by pests that might cause both qualitative and quantitative loss to crops. The least contaminant was malathion with an average mean concentration of 40.8 μg kg–1. The observed trend in concentration of studied OPPs were dimethoate (36.8%) > diazinon (14.3%) > parathion methyl (12.3 %) > parathion ethyl (20.3%) > chlorpyriphos (14.0%) > malathion (9.9 %). The EU order of percentages of OPPs above MRLs is as; cabbage (24.8%) > cauliflower (13.6%) > broccoli (11%) 17 > cauliflower (13.6%) > lettuce (4.0%) > spinach (3.7%) > celery (1.8%) > mustard (1.8 %). Various factors are responsible for OPPs residue greater than MRLs. Some of these factors are lack of safety education and awareness about harvesting, pesticides treatment procedures, application dose and appropriate time (Sapbamrer and Hongsibsong, 2014). As most of the farmers are illiterate, they usually do not follow the labeled instructions. PYRs have less photostability, greater insecticidal activity, and relatively low toxicity as compared to OPPs. Its concentration in crops decreases in the order; cabbage > cauliflower > lettuce > celery > spinach while in broccoli and mustard it was not detected. It is clear that not all vegetables were contaminated by PYRs and cabbage seemed to be the most affected one. The concentration of all these PYRs were in the range of ND–1.6, ND–16.7, ND–6.6, ND–10.0 and ND–100 μg kg–1 in mustard, lettuce, celery, cauliflower and cabbage respectively. Among PYRs, fenvelerate was abundantly found, the sum of its average mean concentration in all vegetable samples was 20.2 μg kg–1 and cabbage was found to be the most contaminated. In spinach and broccoli, it was not detected while mustard was the least contaminated. Only one sample of cabbage has crossed the MRL value. The observed trend in concentration of OPPs in this study was fenvelerate (29.8%) > permethrin (7.7%). The difference in its concentration might be due to its different application rates at different sites on different vegetables or fast degradation of permethrin on these vegetables.
Risk Assessment
Health risk estimates associated with the total of 80 samples (cabbage, cauliflower, broccoli, spinach, lettuce, celery and mustard) was analyzed for OCPs, OPPs and PYRs (Table 2) for each vegetable by considering the mean concentration for each pesticide in the vegetables. Table 2 comprises estimated daily intake (EDI), reference daily dose (RDD) and average maximum daily intake and corresponding hazard quotients (HQs) during the study period for both adults and children.
The EDI of OCPs in vegetables ranges as 3.3x10–8–1.0x10–4 for adults and 2.3x10–7–7.8x10–4 for children. For adults the HQs for OCPs in vegetables decrease as broccoli > lettuce > cabbage > cauliflower > celery > mustard > spinach. For children, the maximum THQ decreases as DDT > β-HCH > α-HCH > γ-HCH > endosulphan > DDE >DDD.
The combined risk due to OCPs for adults in vegetables decreases in the order cabbage (0.2) > cauliflower (0.09) > broccoli (0.05) > celery (0.03) > lettuce (0.02) > mustard (0.005) > spinach (0.003) for children. The combined risk were in the order broccoli (3.0) > cabbage (1.7) > cauliflower (0.6) > lettuce (0.2) > mustard (0.04) > and celery (0.02) respectively. This indicated that children are the most vulnerable group as they eat more of single unit of one food commodity in one day. This might cause a systematic toxicity due to exposure to OCPs [2]. For children the HQs of OCPs in vegetables decreases in the order; broccoli > lettuce > cabbage > cauliflower > mustard > celery > spinach.
For OPPs, the HQs for each of the pesticides in vegetables does not exceed 1.0 though some had residue levels above MRLs. The EDI of OPPs in vegetable sample ranges as 3.3x10–8–3.7x10–5 for adults and 2.3x10–7–3.0x10–4 in children. For adults, the HQs in vegetables decreases in the order; cauliflower > brocolli > cabbage > spinach > lettuce > celery > mustard and for children, cabbage > brocolli > cauliflower > spinach > lettuce > celery > mustard. This is dangerous as cabbage is sometimes eaten in raw form by consumers as a salad. For adults the maximum THQs for OPPs (dimethonate, diazinon, parathion ethyl, parathion methyl, chlorpyriphos and malathion) were 2.5x10–2, 5.3x10–2, 6.8x10–3, 8.1x10–4, 2.3x10–4 respectively. The maximum THQ increased in the order malathion < chlorpyriphos < parathion methyl < parathion ethyl < diazinon < dimethoate. For children the maximum THQ decreases in the order 1.0x10–3, 1.8x10–1, 3.3x10–2, 7x3⋅10–2, 5.7x10–3 and 9.7x10–3. The maximum THQ decrease in the order diazinon > dimethoate > parathion methyl > parathion ethyl > malathion > chlorpyriphos. The average THQ in children decrease in the same order as for adults.
The combined risk due to OPPs for adults in vegetables decreased in the following order cabbage (0.6) > cauliflower (0.4) > celery (0.1) > broccoli (0.06) > lettuce (0.01) = spinach (0.01) > celery > mustard (0.004) and for children cabbage (4.3) > cauliflower (2.0) > brocolli (1.7) > lettuce (1.4) > spinach (0.1) > celery (0.09) > mustard (0.02). The highest HQ was that of diazinon and dimethoate of 0.47 and 0.2 respectively. Diazinon is an acetylcholinesterase inhibitor and neurotoxicant and had the lowest ADI among all other studied pesticides. It is believed that lower level of enzymes might increase the susceptibility of children to neurotoxicity via OPPs exposure (Yu et al., 2016). Its higher HI might cause an adverse health effect on inhabitants in the study area specially farmers who are directly exposed to it. They might suffer from blurred vision, respiratory problems, muscle weakness and pulmonary edema, and its severity varies with the exposure dose and duration (Jaipieam et al., 2009). The presence of higher concentration of dimethoate might cause malignant brain tumors in farmers as reported previously (Sinha et al., 2012). In Kashmir, where farmers suffered from brain tumor due to exposure of multiple neurotoxic and carcinogenic mixture of OPPs, which might also result in Parkinson disease. However, the hazard Indices (HIs) of OPPs (cumulative risk) was > 1.0 in children (1.4) than adults (0.4) indicating that children are exposed to health risk via consumption of these vegetables since many vegetable samples contained more than one OPPs. These results are in contrast to studies in Ghana and China (Akoto et al., 2015; Yu et al., 2016), where combined health risk for OPPs was < 1.0. Vegetables are the main route for exposure to OPPs of local people. It can bioaccumulate in the human body in cases of continuous exposure causing long lasting neurobehavioral impairment due to accumulation of neurotransmitters, acetylcholine, at nerve terminals (Chen et al., 2011) therefore, a continuous environmental monitoring and health survey should be conducted to prevent the possible future risks with OPPs. This study is also helpful in facilitating a risk assessment for children’s health due to higher OPPs in vegetables.
In the case of PYRs, HQs were very low indicating its less contamination of vegetables. For adults the HQ values for PYRs decrease in the order of cauliflower > cabbage > celery > mustard and was absent in broccoli, spinach and lettuce. The maximum THQ in adults were 8.3x10–3 for fenvelerate and 6.6x10–3 in children. The combined health due to PYRs via consumption of vegetables for adults decreases in the order cabbage (8.3x10–3) > cauliflower (1.9x10–3) > celery (4.1x10–4) > lettuce (1.4x10–4) > mustard (1.2x10–4) and for children cabbage (5.8x10–2) > cauliflower (7.1x10–3) > lettuce (1.0x10–3) > celery (2.9x10–4) > mustard (8.7x10–5). For children, the HQs decreases as cauliflower > cabbage > celery and mustard. The highest quotient (HQ) index was that of fenvelerate (0.005). The His (cumulative risk) for adults was 0.01 and for children it was 0.01. The highest HQs for OCPs were 32.7 and 30% in adults and children, in OPPs were 65 and 69.5% for adults and children, and for PYRs as 1.6 and 0.5%. OPPs like diazinon are carcinogenic and mutagen an endocrine disruptor effecting the reproductive development (Vijgen et al., 2011). OCPs like ɣ-HCH could pose toxicity by effecting the endocrine system, causing cancer, and bioaccumulation due to its toxicity by persistence (Vijgen et al., 2011). The results provided important information regarding the contamination level and toxicity of OPPs in one of the important agricultural area of Malaysia, and needs an urgent action for appropriate use of pesticides on vegetable.
PCA analysis was used to identify the sources of pollutants. Principal component 1 (PC1) accounted for 38.1 % of data variability and is related to DDTs, chlorpyriphos and fenvelerate indicating that they are coming from the same sources. PC2 contains 21.7% of data variability and its main contributors were ɣ-HCH, endosulphan and parathion ethyl. PC3 (17.9% variance) highlights the combination of α-HCH and parathion ethyl. PC4 (11.8% variance) includes α-HCH, β-HCH and permethrin and PC5 (8.6% variance) α-HCH, parathion methyl and malathion (Table 4). These observations indicated that; (i) farmers are using mixtures of pesticides over the same crop; (ii) vegetables in the field are laying side-by-side and (iii) high rotation frequency. The biplot indicates that vegetables like cabbage, spinach, cauliflower and celery lie close together and contaminated by the majority of pesticides as compared to broccoli, lettuce and mustard. These observations again signify the importance of pesticides application on crop type (Figure 1).