Exposure of Rana ridibunda to lead I. Study of lead accumulation in various tissues and hepatic delta-aminolevulinic acid dehydratase activity.

There are few data at present on the impact of lead (Pb) on amphibians, although declines in amphibian populations due to man-made changes in the environment have been recorded in recent years. The impact of Pb in adult frogs, Rana ridibunda, was therefore examined. Animals were exposed to 14 mg l(-1) (ppm) aqueous Pb [as Pb(NO3)2] for 4, 10 and 30 days. The chosen Pb concentration corresponded to one-tenth of the 96-h LC50 value for Pb (138.18 ppm). We measured the Pb content of the liver, kidneys, ventral skin and gastrointestinal (GI) tract, and the activity of hepatic delta-aminolevulinic acid dehydratase (delta-ALA-D). Gross morphological characteristics of the frogs were not affected by Pb accumulation in their tissues. At the end of the 30 days of exposure all tissues accumulated Pb. The accumulation of Pb in the liver, kidneys and ventral skin was correlated positively with the time of exposure. The Pb concentration in the GI tract reached a plateau at day 10 and there was no significant increase of Pb in the liver after day 10, suggesting excretion of Pb. The activity of hepatic delta-ALA-D decreased by 90% on day 30 compared to control values. The decrease of hepatic delta-ALA-D activity was correlated negatively with the concentration of Pb in liver and the time of exposure. This study suggests that the hepatic delta-ALA-D activity can be used as a biomarker of Pb intoxication for this species.