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Blood lead concentrations in free-ranging Nile crocodiles (Crocodylus niloticus) from South Africa

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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.

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Acknowledgments

We thank R. Taylor, P. Calverley, G. Champion, F. Myburgh, S. Kyle and family, the many volunteers who assisted with fieldwork, M. Dreslik for statistical guidance, Ezemvelo KwaZulu-Natal Widlife and the iSimangaliso Wetland Park Authority. The Ford Wildlife Foundation and the South African Water Research Commission are thanked for their vehicle/financial support.

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Authors and Affiliations

  1. School of Life Sciences, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, 3209, South Africa

    Jonathan K. Warner, Xander Combrink & Colleen T. Downs

  2. Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, 0110, South Africa

    Jan G. Myburgh

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  1. Jonathan K. Warner
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Correspondence to Jonathan K. Warner.

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All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted. This article does not contain any studies with human participants performed by any of the authors.

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Warner, J.K., Combrink, X., Myburgh, J.G. et al. Blood lead concentrations in free-ranging Nile crocodiles (Crocodylus niloticus) from South Africa. Ecotoxicology 25, 950–958 (2016). https://doi.org/10.1007/s10646-016-1652-8

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