ALA-D and ALA-D reactivated as biomarkers of lead contamination in the fish Prochilodus lineatus

ALA-D activity and lead concentrations were measured in blood and liver tissues of the fish Prochilodus lineatus, collected from three locations along the coast of the La Plata River, Argentina. Two of them, Berazategui and Berisso, were located nearby the main ducts that discharge the urban and domestic waste disposal from Buenos Aires and La Plata cities, respectively, while the third station (Atalaya) was free of sewage discharges. For both tissues, the levels of lead in fish from Berazategui and Berisso were higher than those found in the samples from Atalaya. For blood, but not for liver, a significant negative correlation was found between ALA-activity and tissue levels of lead considering all the data. However, no good correlations were observed at each location. Therefore, an enzyme reactivation technique was optimized. The blood enzyme, but not the liver one, could be effectively reactivated with zinc (ZnII). The values of the reactivated ALA-D in samples from Berazategui and Berisso, but not from Atalaya, were significantly higher than the original values, indicating that the enzyme was actually inhibited. In addition, the reactivation index showed significant correlations with the blood lead levels. It is proposed that the reactivation index, rather than the ALA-D activity, may reflect better the extent of lead contamination, especially for field monitoring programs where many confounding factors may affect the biomarker response.