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

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.

Nondestructive Evaluation of Metal Bioaccumulation and Biochemical Biomarkers in Blood of Broad‐Snouted Caiman (Caiman latirostris) from Northeastern Brasil

“…Basal concentrations from AF are within the range reported for control animals by Camus et al (1998; Table 3). The highest mean Pb blood of 0.83 µg mL -1 detected in animals from UA is similar to the reported high doses in A. mississippiensis in Louisiana (Camus et al, 1998) and lower than blood Pb concentrations in male C. niloticus from South Africa (Humphries et al, 2022;Warner et al, 2016), where toxic effects were considered likely (Table 3). For birds, Pb levels of intoxication have varied from subclinical (0.5 µg mL -1 ) to severe clinical intoxication (1 µg mL -1 ; Pain et al, 2019) and for mammals, intoxications have occurred from 0.6 to 0.8 µg mL -1 (Ma, 2011).…”

Relationships between stable isotopes and trace element concentrations in the crocodilian community of French Guiana

“…Consequently, trace elements such as Hg and Pb among others, accumulate in crocodilian tissues (Jeffree et al, 2001;Almli et al, 2005;Warner et al, 2016;Quintela et al, 2020).…”

Freshwater aquatic reptiles (Testudines and Crocodylia) as biomonitor models in assessing environmental contamination by inorganic elements and the main analytical techniques used: a review

“…The literature explains that males, females and juveniles store inorganic elements in different ways (Schneider et al, 2011), but sex has generally been shown to be non-significant in many studies on turtles and crocodilians (Burger et al, 2009;Schneider et al, 2011;Warner et al, 2016). In articles where there is a significant difference in the sex parameter, the authors explain that males may have higher levels than females due to the freeing of small quantities of these elements through eggs by females during nesting and oviposition processes (Delany et al, 1988;Schneider et al, 2011).…”