Effect of the co-exposure to organophosphate pesticides and noise on the auditory function of farm workers

摘要

On a daily basis, farmers use mobile and fixed machinery generating noise levels from 85 to 120 dBA (EU-OSHA 2008; Health and Safety Executive 2009). Therefore, it is not surprising that noise-induced hearing loss is common among farmers (Plakke & Dare 1992; Hwang et al. 2001; McBride et al. 2003). However, noise is rarely the sole contaminant in most work settings (Campo et al. 2009). Studies have demonstrated that concomitant exposure to noise and a variety of chemicals (solvents, as-phyxiants, heavy metals, pesticides) increases the risk and/or severity of acquiring hearing loss (Campo et al. 2009; Johnson & Morata 2010; Vyskocil et al. 2011). Furthermore, organic solvents can by themselves produce otoneurotoxic effects in both humans and experimental animals (Vyskocil et al. 2009). Farmers use a variety of pesticides, among other methods, to manage pests. Organophosphate insecticides (OPs) are widely used worldwide in agriculture and horticulture because of their efficacy and rapid degradation (Maroni et al. 2000). Within this category of pesticides, frequently encountered active ingredients are malathion, chlorpyrifos, terbufos, diazinon and parathion-methyl (U.S. EPA 2004). OPs are known neurotoxic substances (Hawkers et al. 1989). They exert their neurotoxic action through the inhibition of nervous system acetylcholinesterases (AChE), enzymes responsible for the degradation of acetylcholine (ACh) at nerve junctions (Koelle 1994; Sidell 1994).