Relationships between blood lead and indicators of effect in cows environmentally exposed to lead.

Biological indicators of lead exposure and its effects were measured in 83 cows from a lead-contaminated area in the vicinity of a lead smeltery and in 53 cows from a control area. Differences between the groups were highly significant for blood lead (PbB) content, activity of erythrocyte delta-aminolevulinic acid dehydratase (ALAD) and erythrocyte protoporphyrin (EP) content, but considerably less significant for blood hemoglobin (Hb) content and not significant for hematocrit (Hct). An exponential, rather than linear, characteristic form was observed for the relationships between ALAD activity, EP, Hb and Hct with respect to PbB. This finding supports the hypothesis that lead-induced effects are dependent on the long-term integrated level of lead exposure, rather than the recent lead exposure level as mainly reflected by PbB. The use of ALAD activity and EP as cumulative lead exposure indicators is suggested.