Abstract:
Generally crocodilians have received little attention with regard to the effects of lead
toxicity despite their trophic status as apex, generalist predators that utilize both aquatic
and terrestrial habitats, thereby exposing them to a potentially wide range of environmental
contaminants. During July–October 2010 we collected whole blood from 34 sub-adult and
adult free-ranging Nile crocodiles (Crocodylus niloticus) from three separate populations in
northeastern South Africa in order to analyze their blood lead concentrations (BPb).
Concentrations ranged from below detectability (<3 μg/dL, n = 8) to 960 μg/dL for an adult
male at the Lake St Lucia Estuary. Blood lead concentrations averaged 8.15 μg/dL (SD = 7.47)
for females and 98.10 μg/dL (SD = 217.42) for males. Eighteen individuals (53 %) had
elevated BPbs (≥10 μg/dL). We assessed 12 general linear models using Akaike’s Information
Criterion (AIC) and found no significant statistical effects among the parameters of sex,
crocodile size and population sampled. On average, crocodiles had higher BPbs at Lake St
Lucia than at Ndumo Game Reserve or Kosi Bay, which we attribute to lead sinker ingestion
during normal gastrolith acquisition. No clinical effects of lead toxicosis were observed in
these crocodiles, even though the highest concentration (960 μg/dL) we report represents
the most elevated BPb recorded to date for a free-ranging vertebrate. Although we suggest
adult Nile crocodiles are likely tolerant of elevated Pb body burdens, experimental studies
on other crocodilian species suggest the BPb levels reported here may have harmful or fatal
effects to egg development and hatchling health. In light of recent Nile crocodile nesting
declines in South Africa we urge further BPb monitoring and ecotoxicology research on
reproductive females and embryos.
