Biomonitoring of pesticides exposure and the fate of pesticides use among smallholder vegetable producers in Tanzania

Abstract

This study assessed drivers of increased and changing patterns of pesticide use, levels of Acetylcholinesterase (AChE) inhibition, associated health effects and co-exposure risks of pesticide residues and bacterial contaminants in fresh vegetables. A total of 613 vegetable samples were collected from Arusha, Kilimanjaro, Manyara, Dar es Salaam, Morogoro and Iringa, regions. Binary probit models were used to analyze factors fostering increased pesticide use, determinants of pesticide exposure and risks of co-exposure. Significant results were accepted at p < 0.05. Results revealed that most farmers (88.9%) were unaware of pesticide safety practices. Compared with previous studies, there was increased trend in pesticide use (58.4%), which was accompanied by changing pesticide formulations. The number of crops grown (p = 0.002), pesticide mixing (p = 0.012) and region (p = 0.001) contributed positively to likelihood for increased pesticide use. Smallholder farmers were found to be occupationally exposed to pesticides, where exposed farmers had significantly lower AChE levels. The number of exposure symptoms (14.10±7.70) was higher in exposed than unexposed farmers. Self-reported symptoms were also confirmed to correlate with lower AChE and the use of personal protective equipment did not significantly reduce exposure. Women, younger and older farmers, underweight, overweight, and obese farmers were at increased risk of pesticide exposure. Moreover, locally produced fresh vegetables were highly contaminated with pesticide residues, 47.5% had detectable levels of pesticide residues, 74.2% of which recorded average residue levels above Codex Maximum Residue Levels (MRL) standards. Multiple pesticide residues were also detected, these included organophosphates (95.2%), organochlorines (24.0%), pyrethroids (17.3%) and carbamates (9.2%), all constituting the main detected pesticide residues. Consequently, bacterial contamination of fresh vegetables was also evident, with prevalence of bacterial contamination being high (63.2%). Enterobacter (55.6%), Pseudomonas aeruginosa (32.4%), E. coli (28.2%), Citrobacter (26.8%), Klebsiella oxytoca (14.8%) and Salmonella (7.7%) were isolated. 46.4% of tested samples were positive for both pesticide residues and bacterial contaminants. Vegetables from farms (60.7%) contained more bacterial contaminants while vegetables with pesticide residues were about twice more likely to be contaminated with bacteria (OR: 2.231; 95% CI: 0.501, 8.802). Findings from this study also showed extensive use of pesticides, bacterial contamination and exposure among small holder farmers. The observed exposure risks pose short and long-term effects on health of both farmers and general population. The contamination levels of pesticide residues and bacterial contaminants could also be perceived as a serious health problem, as most fresh and vegetables recorded values of pesticide residues far above the Maximum Residue Limits (MRLs) with pathogenic bacteria isolated in higher proportions. Maximum Residue Limits were higher in most vegetables that were consumed raw or semi-cooked. There is therefore an urgent need to develop pesticide monitoring and surveillance systems at farmers’ level by educating farmers and promoting the use of greener pesticides to mitigate the health effects of pesticides and bacterial contaminants.