Heavy metal levels in ribbon snakes (Thamnophis sauritus) and anuran larvae from the Mobile-Tensaw River Delta, Alabama, USA

The Mobile-Tensaw River Delta (MTD) drains more than 75% of the state of Alabama and leads into Mobile Bay and the Northern Gulf of Mexico. Although it is a relatively healthy watershed, the MTD is potentially impacted by inputs of contaminants such as heavy metals. The levels of lead, copper, cadmium, and mercury were measured in whole body samples of Eastern Ribbon Snakes (Thamnophis sauritus) collected from the MTD. Lead, copper, and cadmium levels were also measured in anuran larvae (Rana catesbeiana, R. clamitans, and Hyla cinerea). These organisms were chosen because they are abundant in the MTD and are underrepresented in environmental contaminant biomonitoring studies. Ribbon snakes had significantly lower levels of lead, copper, and cadmium compared to whole body levels in anuran larvae, indicating that these metals were not biomagnifying through upper trophic levels. Copper and mercury levels were significantly correlated with age/growth indices in ribbon snakes. Although detectable levels of all metals were found in anuran larvae and ribbon snakes, these levels appear to be less than body burdens that would be associated with toxic effects. Populations of ribbon snakes in our particular collection sites within the MTD appear to be at minimal risk of exposure to toxic levels of metals. However, the MTD contains low- and high-impact areas, and other populations within this watershed could be at higher risk of exposure to heavy metals. We found the Eastern Ribbon Snake to be an excellent snake model for contaminant biomonitoring because of its abundance, reasonable size, and ease of collection.