Dermal exposure determinants : a pesticide exposure assessment approach for developing countries

Abstract

Background: We know little about the levels of exposure to pesticide in subsistence farmers mainly because of lack of easy to use and low cost pesticide exposure assessment methods.

Aim: This thesis aimed to develop a semi-quantitative approach to assess dermal exposure to pesticides relevant for conditions in developing countries.

Methods: Work was carried out with two groups of subsistence farmers. A visual scoring system, based on the assessment of the extent and intensity of fluorescent images, was modified for Nicaraguan conditions and used to estimate the level of exposure to pesticides of the first group of 31 subsistence farmers. The performance of the modifications was assessed by comparing visual score estimates with the residues of pesticides in the skin with different fluorescent intensity. Residues were quantified by means of skin wiping of areas with different fluorescent intensity. Further, 32 pesticide applications were observed in order to identify relevant determinants of dermal exposure to pesticides. The relevance of the determinants was assessed by correlation with the visual score estimates. A method to assess exposure to pesticide under conditions of developing countries was developed. The method, called DERM, combined checklist and expert rating methods: the relevant determinants are evaluated using an algorithm based on the type of transport process and the area of body surface affected; clothing was also included as a protection factor. Ten industrial engineers, who worked as occupational hygienists at the Nicaraguan Ministry of Labor, applied the DERM to 5 videotaped pesticide applications of a second group of subsistence farmers. The inter-rater correlation coefficient was estimated to assess the reliability of DERM.

Results: The modifications to the visual scoring system allows identification of the most frequently contaminated body parts (the back of the trunk, the hands and forearms, the front of the legs and the feet) and give some clues on the mechanisms of contamination (transfer of the pesticide while touching contaminated surfaces, deposition from the air, and emissions from the source). The skin wiping confirmed a good performance of the modifications (r=0.63). The multistep reduction strategy identified 27 relevant determinants of dermal exposure to pesticide. Work practices, spray equipment, and worksite related determinants explained 52, 33 and 25% of the exposure variability; clothing and hygiene practices were weaker determinants and did not always reduce the exposure. The DERM algorithm performed well against the visual scoring system (r=0.69; p<0.01), and was reliable (ICC=0.67; CI95%=0.37-0.9). DERM identified the farmer with the highest exposure and the relevant determinants.

Conclusions: Semiquantitative methods such as the fluorescent tracer and the visual scoring system, and assessment of determinants with a simple algorithm, promise to be good alternatives for exposure assessment in developing countries. The DERM method proved to be reliable and easy to use for the identification of highly exposed farmers and relevant determinants of exposure. Combination of fluorescent tracer technique and DERM may be useful for designing preventive programs to reduce exposure to pesticide.