Exposure of Highland Hmong Villagers to Pesticides in Northern Thailand

Abstract

P-771 Introduction: Change from subsistence farming to production for the market has become common in the developing world. Government restrictions on land use, population growth and demand for manufactured goods caused many highland minority people in northern Thailand to change from traditional “organic” land-extensive, labor-intensive subsistence slash-and-burn to fixed-field production of cash crops with heavy use of pesticides. Previous cross-sectional surveys in 3 rural highland Hmong communities revealed high levels of cholinesterase inhibition (CI) among all ages and both sexes, and suggested seasonal and geographic variations in CI levels. This paper reports associations of seasonal variations in pesticide use with CI levels, chromosome aberrations (CA) and protective behavior among members of randomly selected households in one highland Hmong village. Methods: To study relationships between seasonal variations in pesticide use, CI and chromosome aberrations (CA) and demographic variables we observed and interviewed consenting household heads concerning pesticide use and protective behavior (use of protective clothing, staying out of fields after spray, etc.). We collected finger stick and venous blood from each consenting member of sample households 4 times: April 2002 (the time of highest pesticide use), October 2002 (after pesticide use stopped), January 2003 (3+ months after the last use of pesticides) and April 2003 (when pesticide use was high again). We used a rapid test to measure CI, and measured CA by a WHO standard method. Results: Paired measurements of CI in the same individuals were significantly higher in April 2002 than in October 2002 (after pesticide application stopped) p < .001, and higher in April 2003 than in October 2002 and January 2002 (p < .001). Numbers of cells with chromosome abnormalities in the same individuals were higher in April 2002 than in January 2003 (p = .025). Members of the village population, including women and children who were not actively involved in pesticide application showed similar seasonal variation of CI and CA associated with seasonal use of pesticides, although levels were generally lower among those who do not themselves apply pesticides. Discussion and Conclusions: CI and CA are widespread in this population. CI appears to be largely reversible over time in the absence of pesticide use; CA appears decline after a period of non-use, but does not reach pre-pesticide use levels. Thus CA appears to be cumulative. This suggests long-term and widespread health effects of use of pesticides in this population.