Pesticides are chemicals commonly used in agricultural industries worldwide. After use, pesticide residues contaminated in environments can be hazardous to the health of consumers and farmers. In 2020, Thailand imported agricultural chemicals approximately 900,000,000 US$, accounting for 40% growth rate compared to 2019 . The most common pesticides are organophosphates (OPPs), which many farmers have used without appropriate handling [2,3]. OPPs extinguish insects by inhibiting acetylcholinesterase (AChE), an enzyme hydrolyzing the neurotransmitter acetylcholine (Ach) into choline and acetate after activation of acetylcholine receptors (AChRs) at the postsynaptic membrane. This inhibition results in overstimulation of the neuromuscular system. Bioaccumulation of OPP in the human body is manifested by reduced blood AChE level. Acute OPP toxicity causes diarrhea, vomiting, muscle tremors, and confusion . Chronic accumulation of low doses of OPPs is associated with neurotoxicity, anxiety, and metabolic diseases [5, 6].
In principle, every pesticide has a pre-harvest interval (PHI), the number of days required to lapse between the final pesticide application date and the harvest date . On the harvest day, it is required that detectable concentration of the pesticide must be below the maximum residue limits (MRLs, expressed in µg/kg), the highest levels of residues expected to be found in food products when the pesticide is used following its label, set by the Food and Agriculture Organization-World Health Organization (FAO-WHO) . The PHI values are different among types of OPPs and crops. For example, PHIs of quinalphos in yard long bean, eggplant, and cabbage are 7, 10, and 12 days after spraying (DAS), respectively. Meanwhile, PHIs of malathion are 7 DAS for yard long bean and eggplant, but 10 DAS for cauliflower . However, the PHI in vegetables is maximally 12 DAS. Based on the PHIs reported by the study of Prodhan and colleagues, the toxicity levels of pesticides in vegetables have been categorized into 4 groups, i.e., 0-2 days = highly toxic, 3-7 days = moderately toxic, 8-14 days = slightly toxic, and 15-30 days = non-toxic .
Our previous study showed that OPP contamination in the blood of vegetable farmers was not associated with their knowledge and behaviors on pesticide use despite the high rate of risk and unsafe blood AChE levels . To this end, however, details of PHIs, specific knowledge and behaviors related to pesticide use and cropping, and possible poisoning symptoms have not been reported. Therefore, this research was aimed to investigate the association of health problems, health knowledge, and behaviors with levels of OPP contamination in the blood of vegetable framers in the local community of Thailand.
Materials and Methods
Study design, participants, and ethical issue
Participants in this cross-sectional research were 219 vegetable farmers from Kosumphisai, Chuenchom, and Kantarawichai districts, Maha Sarakham, Thailand. Inclusion criteria were 1) age ≥ 18 years old, and 2) being vegetable farmers. All procedures have been voted by 2 reviewers, approved by the Mahasarakham University Ethics Committee for Research Involving Human Subjects, and endorsed by the chairperson Asst. Prof. Ratree Sawangjit (No.127/2020).
The questionnaires of 1) knowledge on pesticide uses (Table 1), 2) behaviors on pesticide uses (Table 2), and 3) personal characteristics data were approved for content validity by 3 experts in Nutrition and Occupational Health. The content validity has been confirmed by the index of item-objective congruence (IOC). Only the items with IOC scores ≥ 0.5 were qualified for the questionnaires. The items with Cronbach’s a ≥ 0.7 were accepted and used in the questionnaires.
Blood Sampling and Acetylcholinesterase Level Measurements
To detect AChE in the body from exposure to OPPs, a reactive paper test kit was from The Government Pharmaceutical Organization, Ministry of Public Health, Thailand. Blood samples were taken from a fingertip by public health officers. The paper color changes were compared with the standard and divided into 4 levels of AChE. Suppose the test paper changed to the yellow, yellow-green, green, and blue color. In that case, it can be interpreted to normal, safe, risky, and unsafe levels, respectively as previously shown . Samples were collected from October-December 2020, the spraying and harvesting periods.
The data was employed descriptive statistics, then the relationship of each categorical data was analyzed by c2 tests. The level of statistical significance was P < 0.05. All data were analyzed by SPSS Statistics version 18.
Results and Discussion
Relationship between personal characteristics of vegetable farmers and risk levels of pesticide contamination
Results showed that from totally 219 farmers, 120 participants were aged < 60 years old and 99 were ≥ 60 years old. Further c2 analysis showed that the levels of pesticide contamination in vegetable farmers were significantly associated with age (c2 = 13.54, P-value = .00) and pre-harvest interval (c2 = 21.59, P-value = .01) (Table 3).
Levels of knowledge on pesticide uses
Next, levels of knowledge on pesticide uses were analyzed. There was no significant association between the levels of knowledge and the levels of pesticide contamination (c2 = 4.14, P-value = .24).
Risk behaviors in pesticide uses
The results revealed that the risk levels significantly were associated with the levels of pesticide contamination (c2 = 25.26, P-value < .001) (Table 4). Before using chemical pesticides, the farmers did not read labels and user instructions and mixed pesticides with their bare hands. While using a pesticide, many of them did not note the wind direction. They also did not wear long-sleeved shirts, long trousers, a face mask, shoes, rubber boots, plastic safety goggles, or a full-face respirator mask. After using pesticides, many of them did not clean and store pesticide spraying equipment well away from other household items.
Characteristics of the farmers
The characteristics studied were the gender of the farmer, their age, their educational level, their working experience (in years) with using pesticides, and famer pre-harvest interval (in days). The result characterized factors related to the levels of pesticide contamination of farmers, which were significantly associated with age. The age of farmers was over sixty years old, Srishti Shrestha et al. found that the age-related hypothyroidism risk increased in the farmers who used organochlorine and organophosphate insecticides, particularly in those older than 62 years old . Considering the pre-harvest interval, it was previously found associated with health risks, which signified that too early harvesting of the crops could maintain the presence of pesticides .
Knowledge on pesticide uses
This study discovered that most farmers come upon a high level of knowledge on pesticide use; even though it was not statistically related to the risk of pesticide use. However, some farmers had a low level of knowledge, such as 1) when pesticides splash into farmer's eyes, they can use a handkerchief or tissue paper to wipe it away, 2) immediately (within 10 min) after spraying pesticides, a farmer should not drink water and wearing a cloth hood over their head while spraying pesticides to prevent their harm. These results were found in several studies in the developing world. This was more disquiet for the farmers and field workers’ exposure to pesticides . It also occurred similarly in China – some Chinese farmers also lacked knowledge on pest management and pesticide use correlated with their excessive pesticide use .
Risk behaviors in pesticide uses
The risk levels were significantly associated with the levels of pesticide contamination. It indicated that high mean scores during spraying were also serious issues. While the farmers took a break; they were: 1) eating food, 2) smoking tobacco, 3) chewing betel, and 4) drinking alcohol. A similar study in Nepal found an association of the safe practice of chemical pesticides with farmers’ knowledge and perception factors .
In conclusion, contamination levels of OPPs are associated with older adulthood, pre-harvest interval, and risky behaviors. Farmers over sixty years old might have a longer time of OPP exposure, posting higher risks of pesticide contamination. In addition, farmers should harvest their crops after spraying for 15 days. Furthermore, farmers should avoid oral ingestion of OPPs during spraying. These factors should be monitored and aware of in vegetable farmers in these local areas of Thailand. They should be educated on safety protocols in pesticide use.
This work was financially supported by the Faculty of Public Health, Mahasarakham University. The authors would like to thank local authorities and farmers for their cooperation.
Potential Conflicts of Interest
The authors declare no conflict of interest.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
All authors contributed toward data analysis, drafting, and revising the paper and agreed to responsible for all the aspects of this work.
Conflict of Interest
We have no conflicts of interest to disclose.
HOW TO CITE THIS ARTICLE
Wisit Thongkum, Nachalida Yukalang, Niruwan Turnbull, Kallaya Harnpicharnchai, Kloyjai Singsuwan, Lapasrada Chiarawattanasakun, Akom Ruttawongsa, Kukiat Tudpor. Pesticide Contamination in Blood of Vegetable Farmers is Associated with Age, Pre-Harvest Interval, and Risk Behaviors, J. Med. Chem. Sci., 2022, 5(4) 624-630