Pesticide use in Nepal : The assessment of residues and risk

Bhandari, Govinda


My PhD thesis evaluates chemical pesticides that are used in agriculture to protect crops from pests and diseases. The thesis presents a perspective of pesticide use among Nepalese farmers and pesticide retailers. Furthermore, the thesis identifies pesticide residues in Nepalese vegetables and their soils and assesses health and environmental risk.

A study was carried out in the Gaidahawa Rural Municipality of Rupandehi district, Nepal. The objectives were (i) to estimate pesticide use in vegetables and identify the factors affecting the safety behaviour of farmers and pesticide retailers on pesticide use and handling; (ii) to assess the dietary risk to humans from pesticides in vegetable crops that were exposed to the highest doses of pesticides in the field; (iii) to identify the human health risks from non-dietary intake of pesticides present in agricultural soils; and (iv) to investigate the ecological risk of pesticides detected in soils from both IPM and conventional fields. The objectives have been addressed in four separate interconnected studies in Chapters 2-5.

Chapter 2 of this thesis aimed to examine pesticide use in a rural area of Nepal. We looked at pesticide use on vegetable crops and identified factors affecting the safety behaviour of farmers and pesticide retailers. Farmers perceived that pesticides posed low threats to humans and ecosystems. Due to the perceived lower threats from pesticides, farmers perceived that the use of personal protective equipment (PPE) had low benefits and high barriers such as unavailability and discomfort while using. Likewise, for retailers, perceived threat and cues to action affected their safety behaviour. Farmers applied the highest amount of organophosphate insecticides and carbamate fungicides on eggplants, chillies and tomatoes. The illegal import of chemical pesticides (including banned pesticides) in and around the border areas in Nepal is running rampant. Most farmers perceived pesticides as a “medicine” and not a poison since pesticides cured plant diseases. This Chapter recommends that more educational activities be made available to farmers and retailers. These educational activities could include organizing pesticide-related documentaries and talk shows, broadcasting news via the radio, television, newspapers and mobile applications in order to increase the levels of knowledge and awareness among farmers and retailers.

The study in Chapter 3 presents data of 23 pesticide residues, including their metabolites, in 3 vegetable crops: chillies (n=27), tomatoes (n=32) and eggplants (n=27). We used our results to assess the possible health risks from dietary exposure to pesticides. The study detected 14 different pesticide residues, including insecticides and fungicides, in the vegetables. The study assessed adults’ and adolescents’ dietary risk of those pesticides. The study adopted EFSA’s risk assssment methods: hazard quotient (HQ) and hazard index (HI). We detected residues of pesticides in over 90% of the sampled eggplant crops and 100% of the sampled tomato and chilli. One individual tomato sample from conventional farming system contained up to 7 different residues, forming pesticide cocktails. Our results showed that the adoption of IPM farming may significantly reduce pesticide residues in vegetables. Of all the vegetables and pesticides, carbendazim in tomatoes was high (p <0.05). The dietary risk assessment showed that the consumption of tomatoes could impose an acute risk from triazophos and chlorpyrifos for adults and adolescents. This Chapter recommends strengthening legal frameworks and offering alternative programs that support food safety. It recommends to either ban or strongly restrict the use of triazophos and chlorpyrifos in tomatoes. We also suggest the adoption of IPM farming to assure the safety of vegetables meant for human consumption.

The study in Chapter 4 aimed to assess non-dietary risk due to pesticide residues in soils by examining three major exposure pathways in humans: dermal contact, direct ingestion, and inhalation. We measured the concentration and distribution of pesticides at three depths (0-5 cm, 15-20 cm and 35-40 cm) of soil samples (n=147) from 2 farming types: integrated pest management (IPM) and conventional. Hazard quotient and hazard index were used to characterize non-cancer risk in adults and adolescents. We used the USEPA models to assess cancer risk based on the average daily dose of pesticide exposure via the different exposure routes. We found pesticide residues more frequently in upper layers of soil (0-5 cm). We detected up to 7 residues in an individual soil sample from conventional farming. Soils from eggplant fields had a higher number of pesticide residues (p <0.05) than tomato fields. Likewise, soils from conventional farming had a significantly higher number of pesticide residues (p <0.05) than the soils from IPM farming. TCP and chlorantraniliprole residues were detected the most frequently. Of all tested pesticides and their degradation products (n=23), we detected 15 in soils, where chlorpyrifos and p,p’-DDT residues were found to be in the highest concentrations. Overall, the human health cancer and non-cancer risks posed by the pesticides in soils was negligible. This Chapter recommends promotion of IPM methods for reducing pesticide pollution in soils.

Chapter 5 assesses ecological risk of pesticides (n=9) at 3 depths of soil. We adopted globally used methods for risk assessment such as toxicity exposure ratio (TER) and risk quotient (RQ). We estimated risk for EFSA’s soil organisms such as earthworms (Eisenia fetida), enchytraeids (Enchytraeus crypticus), springtails (Folsomia candida), mites (Hypoaspis aculifer) and nitrogen and carbon mineralization microorganisms. We made a comparison between the measured pesticide concentrations in soils and the pesticide permissible concentration (or the soil regulatory guidance value for pesticides whose RQ and TER could not be calculated). Profenofos, imidacloprid and chlorpyrifos showed a higher risk (RQ>1) at 2 depths (0-5 cm and 35-40 cm), 1 depth (35-40 cm) and 3 depths (0-5 cm, 15-20 cm and 35-40 cm), respectively. The TER of chlorpyrifos was <5 at all depths of soil which posed a chronic risk for F. candida. About 16% of the sites posed ecological risks, determining chlorpyrifos to be a main soil pollutant. The risk at sites increased significantly when farmers had poor pesticide knowledge and waste management practices.