Biomonitoring Heavy Metal Pollution Using an Aquatic Apex Predator, the American Alligator, and Its Parasites

<div><p>Monitoring the bioaccumulation of chemical elements within various organismal tissues has become a useful tool to survey current or chronic levels of heavy metal exposure within an environment. In this study, we compared the bioaccumulations of As, Cd, Cu, Fe, Pb, Se, and Zn between the American alligator, <i>Alligator mississippiensis</i>, and its parasites in order to establish their use as bioindicators of heavy metal pollution. Concomitant with these results, we were interested to determine if parasites were more sensitive bioindicators of heavy metals relative to alligators. We found parasites collectively accumulated higher levels of As, Cu, Se, and Zn in comparison to their alligator hosts, whereas Fe, Cd, and Pb concentrations were higher in alligators. Interestingly, Fe levels were significantly greater in intestinal trematodes than their alligator hosts when analyzed independently from other parasitic taxa. Further analyses showed alligator intestinal trematodes concentrated As, Cu, Fe, Se, and Zn at significantly higher levels than intestinal nematodes and parasites from other organs. However, pentastomids also employed the role as a good biomagnifier of As. Interestingly, parasitic abundance decreased as levels of As increased. Stomach and intestinal nematodes were the poorest bioaccumulators of metals, yet stomach nematodes showed their ability to concentrate Pb at orders of magnitude higher in comparison to other parasites. Conclusively, we suggest that parasites, particularly intestinal trematodes, are superior biomagnifiers of As, Cu, Se, and Zn, whereas alligators are likely good biological indicators of Fe, Cd, and Pb levels within the environment.</p></div

Ratio of bioaccumulation levels (Cparasite/Chost) between alligators and their parasites collectively among geographic zones.

<p>High ratios are indicative of acute exposure to heavy metals, and low ratios are indicative of chronic exposure to heavy metal pollution.</p

Comparative data of the total heavy metal concentration from Lake Loochloosa, FL during (a) 2011, and (b) 2012 alligator harvests.

<p>Each graph represents an individual collected from that year selected at random.</p

Statistical comparison by region (SELA, SWLA, and FL) of heavy metals from different parasite groups.

<p>^a Heavy metal bioaccumulation statistically higher in SELA</p><p>^b Heavy metal bioaccumulation statistically higher in SWLA</p><p>Statistical analyses were performed with Kruskal-Wallis chi-squared tests; region highlighted in table had significantly higher concentrations compared to other areas.</p

Comparison between geographic zones of mean (± standard deviation) heavy metal concentrations (mg/kg) from alligators and their parasites.

<p>Comparison between geographic zones of mean (± standard deviation) heavy metal concentrations (mg/kg) from alligators and their parasites.</p

Average heavy metal concentrations (mg/kg) in alligators and parasites (mean ± standard deviations).

<p>Average heavy metal concentrations (mg/kg) in alligators and parasites (mean ± standard deviations).</p

Summary of parasite species collected from each alligator host/year in each geographic zone.

<p>* Numbers and letters under column “Host” identifies the tag of each alligator individual, i.e., “Alligator 13 2009,” Alligator A 2009”, etc.</p><p>Summary of parasite species collected from each alligator host/year in each geographic zone.</p

Comparative data of As concentrations among pentastomids from SWLA, SELA, and FL.

<p>Quantity of pentastomids analyzed from each region is shown (n =).</p

Map of collection sites in Louisiana West Zone (triangles), Louisiana East Zone (circles), and Florida (rectangles).

<p>Map of collection sites in Louisiana West Zone (triangles), Louisiana East Zone (circles), and Florida (rectangles).</p

Comparative data of the total heavy metal concentration from an individual alligator from Iberville, Louisiana from the 2011 SELA alligator harvest.

<p>Comparative data of the total heavy metal concentration from an individual alligator from Iberville, Louisiana from the 2011 SELA alligator harvest.</p