Objective: in March 2005, the Italian National Monitoring System on Chemical Residuals in Food of Animal Origin detected levels of the pesticide beta-hexachlorocyclohexane (ß-HCH) that were 20 times higher than the legal limit of 0.003 mg/kg in bulk milk from a dairy farm in the Sacco River valley. ß-HCH, a lindane isomer and possible human carcinogen, was subsequently found in milk from several neighboring farms. A study was therefore undertaken to evaluate the extent and risk factors for contamination.
Design: all dairy cattle farms in the valley were enrolled in a retrospective cohort study and their bulk milk analyzed for ß-HCH. A questionnaire was administered to farmers to evaluate possible exposure factors.
Setting and participants: cases: dairy farms with at least one result indicating ß-HCH ≥ 0.002 mg/kg in bulk milk during the period april-june 2005; exposure: feeding animals on fodder cultivated in soils watered with and/or flooded by river water; participants: IZSLT, RMG Local Health Unit, FR Local Health Unit.
Main outcome measures: attack rate, relative risk, attributable proportion among exposed.
Results: of 244 farms tested, 34 met the case definition (attack rate 14%). The exposure to fodder cultivated in soils watered with and/or flooded by river water was observed in 33/34 (97%) case-farms and in 23/210 (10.9%) of those with contamination <0.002 mg/kg in bulk milk (RR 110.8; 95%CI 15.5- 792). Attributable proportion among exposed was more than 99%.
Conclusion: fodder cultivated near a contaminated river was the main risk factor for ß-HCH contaminated milk. On the basis of the epidemiologic evidence and laboratory testing, watering local fields with river water and production of fodder in farms with contaminated soil was banned, and all the animals from positive farms were culled.