Organophosphorus pesticide residues in milled rice (Oryza sativa) on the Chinese market and dietary risk assessment

Abstract

The present study investigates the occurrence of acetylcholinesterase (AChE)-inhibiting organophosphorus (OP) pesticide residues in milled rice samples obtained form local markets in China during the period 2004–2006 and estimates their cumulative exposure. Concentrations of OP pesticides were determined by gas chromatography with flame photometric detection (GC–FPD). The results showed that 9.3% of the samples contained detectable residues of at least one of the seven target OP pesticides (chlorpyrifos, dichlorvos, omethoate, methamidophos, parathion-methyl, parathion and triazophos) mainly used for agriculture in China, with concentrations ranging 0.011–1.756 mg kg⁻¹. Rice consumption data was obtained from an individual food consumption survey. Relative potency factors (RPFs) for each pesticide were calculated with methamidophos as the index compound (IC), using 1- or 2-year chronic non-observed adverse effect levels (NOAEL) for AChE inhibition, mostly in rat brain, obtained from international evaluations of pesticides. Exposure to AChE-inhibiting pesticides for the population above 7 years old at P99.9 represented 52–94.5% of the acceptable daily intake (ADI) expressed as methamidophos. Estimated exposure for children aged 2–4 and 4–7 years at P99.9 were 119 and 104.3% of the ADI level, respectively. This study suggests that a yearly monitoring program for OP pesticide residues and strict implementation of the national safety standard for milled rice is necessary.

Keywords:

• organophosphorus pesticide residues
• milled rice
• relative potency factor
• Monte Carlo model
• daily intake assessment

Acknowledgement

We thank Dr Fen Jin and Tianjin Chen (Institute of Quality Standards and Testing Technology for Agro-Products, Chinese Academy of Agricultural Sciences) for fruitful discussions.