Hair as a matrix for biomarkers of pesticide exposure

The majority of Americans not involved in manufacturing or applying pesticides are exposed to pesticides through dietary intake. Exposure to this portion of the population can be only estimated, using average food consumption profiles and food concentrations of pesticides. Long-term biomarkers of exposure do not currently exist. Hair is a matrix that is an alternative to the more traditional matrices of plasma and urine. Hair may provide an extended sampling time (weeks to months) when compared to plasma and urine (hours to days). In this research, pesticides (and metabolites) of three chemical classes were used to evaluate hair as a matrix. The plasma pharmacokinetic profiles and the time courses of incorporation into hair were determined for DDT, atrazine and malathion. Hair concentrations were measured after 5 days of pesticide administration. The melanin affinities of the pesticides were determined in an in vitro binding study. All compounds, except DDA, were detectable in plasma. Malathion, malaoxon and DDA were not detected in hair. The remaining compounds incorporated equally into pigmented and nonpigmented hair. The hair time-course demonstrated higher concentrations of atrazine, desisoatrazine, DDT and DDE at early postdose times (prior to 2 days). These compounds demonstrated weak affinities for melanin (<~;30% binding). The plausibility of differentiating hair that was externally exposed to pesticides from hair into which pesticides have incorporated from systemic exposure was evaluated. Pesticide-free rat hair was fortified with either DDT and DDE or atrazine and desisoatrazine. Hair collected from dosed rats was pooled and homogenized. Aliquots of were washed with 0.1% SDS and the hair concentrations were compared to the concentrations of unwashed controls. All of the atrazine, desisoatrazine and DDE was removed from the fortified hair after washing; only ~75% of the DDT was removed. Washing also removed ~25-60% of the compounds from the incorporated hair. Hair may be a viable matrix for biomarkers of pesticide exposure. However, not all pesticides may be detectable in hair (as malathion was not). More research is needed with other pesticides and on the ability to detect pesticides in the hair after chronic, low doses.