Lead concentrations in bullfrog Rana catesbeiana and green frog R. clamitans tadpoles inhabiting highway drainages

Abstract

Lead concentrations were determined in sediment and tadpoles of bullfrogs Rana catesbeiana and green frogs R. clamitans from drainages along highways with different daily average traffic volumes (range, 4272 to 108 800 vehicles day⁻¹) and from ponds ≥ 0·4 km from the nearest highway. Lead concentrations (mg kg⁻¹ dry weight) in sediment (7·8 to 940) were usually greater (4–5 times) than those in the tadpoles (bullfrog, 0·07 to 270; green frog, 0·90 to 240 mg kg⁻¹). Lead concentrations in sediment (r = 0·63) and in both species of tadpoles (bullfrog, r = 0·69; green frog, r = 0·57) were positively correlated with average daily traffic volume. Lead concentrations in both species of tadpoles (bullfrog, r = 0·76; green frog, r = 0·75) were also positively correlated with lead concentrations in sediment. At sites where both bullfrog and green frog tadpoles were collected, lead concentrations in the two species were closely related (r = 0·84). Lead concentrations in tadpoles living near highways may contribute to the elevated lead levels reported in wildlife that are potential tadpole predators. Dietary lead concentrations similar to those in our tadpoles have been associated with physiological and reproductive effects in some species of birds and mammals. However, additional data are needed to determine the hazards to predators of lead concentrations in tadpoles.