Background: Commonly consumed vegetables from local markets are considered at a higher risk for organophosphate insecticides (OPs) contamination. This study aimed to investigate the contamination of OP residues in commonly consumed vegetable samples from local markets in 5 provinces, i.e., Nan, Chiang Rai, Lamphun, Lampang, and Chiang Mai provinces located in Northern Thailand. A risk assessment of OPs among adult Thai population was also evaluated by calculating the estimated daily intake (EDI) and the acceptable daily intake (ADI).

Method: The multi cross-sectional studies were conducted in 5 provinces. Twelve vegetables were sampled from main local markets in every district of sampling sides. All samples have analyzed the level of 19 OP residues using GC-FPD. The estimated daily intake and health risk of OP residues were estimated by using hazard index.

Results: Twelve OP residues were detected in 42.8% of the samples, and 16.0% had residue levels that exceeded EU maximum residue levels. The most frequently detected OP residue in the vegetable samples was chlorpyrifos. The percentage of OP contaminated samples slightly increased throughout sampling time, 40.6%, 43.4%, and 47.9%, respectively. Hazard indices (HIs) were calculated based on data from National Health Examination Survey Office and the result showed that HIs of diazinon residue in Pakchoi and dimethoate residue in cucumber were over 1, hence posing a serious threat to human health.

Conclusion: The unacceptable levels of OP residues were observed in all types of vegetables collected from local markets, leading to hazardous exposure among consumers.

Keywords: Health Risk Assessment, Organophosphate Insecticides Residues, Local Markets, Northern Thailand