Environmental contaminants in Texas, USA, wetland reptiles: Evaluation using blood samples

Abstract

Abstract-FourMunicipal Lake received industrial arsenic wastes continuously from 1940 to 1993. Blood samples were analyzed for organochlorines, potentially toxic elements, genetic damage, and plasma cholinesterase (ChE). Dichlorodiphenyldichloroethylene (DDE) concentrations reached as high as 3.0 ppm (wet weight) in whole blood of a diamondback water snake at Old River Slough, a level probably roughly equivalent to the maximum concentration found in plasma of peregrine falcons (Falco peregrinus) in 1978 to 1979 when DDE peaked in this sensitive species. Possible impacts on diamondback water snakes are unknown, but at least one diamondback water snake was gravid when captured, indicating active reproduction. Arsenic was not found in red-eared sliders (only species sampled) from Municipal Lake. Red-eared sliders of both sexes at Old River Slough showed declining levels of ChE with increasing mass, suggesting a life-long decrease of ChE levels. Possible negative population consequences are unknown, but no evidence was found in body condition (mass relative to carapace length) that red-eared sliders at either contaminated site were harmed.

Element Levels in Snakes in South Carolina: Differences Between a Control Site and Exposed Site on the Savannah River Site

“…Overall, these data indicate that the elemental levels in the tissues of water snakes from SRS reported in this study are higher than for many places (Winger et al, 1984;Clark et al, 2000). Unfortunately, there are insufficient data from other studies on the other elements, eliminating the possibility of direct comparisons.…”

“…All the species examined are not limited to an aquatic diet, but also take some terrestrial prey (Conant and Collins, 1998) and the water snakes on SRS eat a variety of prey, including sunfish (Lepomis marginatus), olden shiners (Notemigonus crysoleucas), red-fin pickerel (Exox americanus), pirate perch (Aphredoderus sayanus), green frog (Rana clamitans) and the southern toad (Bufo terrestris, W. Gibbons, personal communication). Cottonmouths may rely on a wider selection of prey, as well as eating snakes and rodents, than the water snakes (Clark et al, 2000). Information on diets thus suggests that cottonmouths should exhibit the highest levels of elements, particularly contaminants, because they are heavier and eat a wider selection of prey (including other snakes which may accumulate contaminants).…”

“…Mean lead concentrations in snakes collected from the downstream Big River sites (6070 and 7520 ppb wet weight, respectively) were significantly higher than those from the upstream, uncontaminated Big River site (190 ppb, wet weight) and the Black River sites (1210, 970, and 150 ppb wet weight). Clark et al (2000), working in Texas, reported mean levels of copper to be 899 ppb (all wet weights) for cottonmouths, and 586-648 ppb for diamondback water snakes; mean mercury was 13.5 ppb for cotton mouths, and 61-146 ppb for watersnakes; mean selenium was 277 ppb for cottonmouths and 318-352 ppb for water snakes; mean zinc was 8880 ppb for cottonmouths, and 13,600-13,900 ppb for water snakes. The snakes in our SRS study has slightly higher levels of copper and selenium, higher levels of mercury, and much higher levels of zinc.…”

“…Levels of organochlorine pesticides, polychlorinated biphenyls and some metals (copper, mercury, selenium, zinc) were examined in blood of diamondback water snakes (Nerodia rhombifer) and blotched water snakes (Nerodia erythrogaster) in Texas (Clark et al, 2000), pesticides in water snakes and cottonmouths from Mississippi (Ford and Hill, 1991), metal concentrations in banded water snakes (Nerodia fasciata) from the SRS (Hopkins et al, 2001), PCBs and organochlorine pesticides in northern water snakes and Lake Erie water snakes (Nerodia sipedon insularum) from the Great Lakes Basin (Bishop and Rouse, 2000), and heavy metals in northern water snakes (Nerodia sipedon) from Tennessee (Burger et al, in press). None of these studies examined three species of aquatic snakes in contaminated and reference sites in both blood and tail snips, although Clark et al (2000) also examined levels in cottonmouths. Blood and tail clips are those being considered for non-destructive bioindicators (see Hopkins et al, 2001;Burger et al, in press).…”

Addressing current knowledge gaps on radionuclide transfer to reptiles

“…Positive correlations have been identified for particular blood, tissue and element combinations, such as mercury concentrations in blood and muscle of Nerodia sipedon (Northern water snakes) [18], and blood sampling may therefore provide an alternative route to investigating element concentrations in adult reptiles. Although blood has been used exclusively by some authors for evaluating contaminant uptake in reptiles [30], blood generally reflects recent contaminant exposure [18] and the complex kinetics of elements within blood [27] are likely to result in high uncertainties.…”