Effects of lead shot pellets contamination on oxidative stress biomarkers and plasma biochemistry in turtles

Abstract

Lead (Pb) shot pellets spent in hunting activities have been accumulated in wetlands worldwide, with densities in the upper 20 cm of wetland sediments above 100 shot/m2 at many locations. Currently, a large number of countries are making significant efforts to reduce or eliminate the input of Pb shot in most wetlands. However, the problem often persists because spent Pb shot remains in soil for 100-300 years. During this time the pellets are slowly buried by sedimentary accumulation, or dissolve over time to disappear, affecting local sediment Pb concentrations. Although studies carried out on the effect of Pb exposure in wildlife through ingestion of pellets accumulated in sediments are numerous, those that address the effect of Pb exposure due to contamination associated with its dissolution in the environment are scarce. In order to fill this gap, we used non-destructive biomarkers to study the exposure and effect of Pb on turtles (Mauremys leprosa and Emys orbicularis) from two Spanish wetlands. The Medina lagoon (ML), where the highest densities of Pb shot pellets of Spain has been described, and Dulce lagoon (DL), a non-contaminated lagoon located in Doñana National Park. The mean whole blood Pb concentration (PbB) from ML turtles was higher than in DL (F1,97=42.541, p<0.01; 29 and 5 ng/ml, respectively), both in males and females (F1,45=20.130, p<0.01; F1,50=26.704, p<0.01, respectively). The δ-aminolevulinic acid dehydratase (ALAD) ratio was negatively related with PbB (F1,93=4.661, p<0.05), regardless of the lagoon or sex. Plasma Total Antioxidant Status (TAS) was positively related with PbB (F1,81=6.723, p<0.05), and also differed with lagoon (F1,81=4.333, p<0.05; higher in DL), and sex (F1,81=5.683, p<0.05, higher in females). Finally, three biomarkers of oxidative stress in red blood cells statistically differed with PbB and lagoon: lipid peroxidation, estimated as thiobarbituric acid-reactive substances (F1,67=7.450, p<0.01; F1,67=14.523, p<0.01, respectively); total sulfhydryl (F1,77=6.387, p<0.05; F1,77=19.982, p<0.01, respectively); and glutathione in oxidized form (F1,63=12.004, p<0.01; F1,63=6.469, p<0.05, respectively). Additionally, the ratio reduced/oxidized glutathione was negatively associated with PbB (F1,63=5.138, p<0.05). Our results evidenced that turtle living in Pb shot contaminated wetlands showed sublethal effects. Nonetheless, further reseach is needed to elucidate Pb effects on individual and population health and dynamics.