Metallic elements in South African sea turtle and crocodile eggs and eggshells
There are concerns about metal concentrations in aquatic and marine environments due to pollution and subsequent bioaccumulation. Contaminants, such as metals and metalloids enter the water environment from industrial processes, urban and suburban runoff, agricultural practices, natural erosion, and geochemical cycles. Once in aquatic systems, these metals may bioaccumulate and biomagnify. One method of observing the effects of metals and metalloids on organisms is by biomonitoring. Biomonitoring of especially long-living species has become an important tool in ecotoxicology; it provides baseline data for further studies into the health of a population, increases our knowledge about the levels of pollution in the ecosystems the animals occupy, provides information for ecosystem-based assessments, priority determinations, and decisions about interventions. Ultimately, biomonitoring might identify sources of pollution. In this study, Nile Crocodile (Crocodylus niloticus), Loggerhead Turtle (Caretta caretta), and Leatherback Turtle (Dermochelys coriacea) eggs and eggshells were used to biomonitor metals and metalloids concentrations. Elemental concentrations in the egg contents and eggshells were established. Comparisons between metal and metalloid profiles were evaluated in order to determine if eggshells could be used as a proxy for egg contents associated with metal and metalloid studies. The possible effects of metals and metalloids on the developing embryo were evaluated. The metal and metalloid concentration in the egg contents and eggshell of marine and fresh water species were also compared. The crocodile eggs and their eggshells were collected from nests inside the Kruger National Park (KNP) and from a crocodile farm. The marine turtle eggs were collected from South African breeding beaches. Eggshells were rinsed with deionized water, air-dried, and powdered. Egg contents were homogenised and lyophilized. Shells and content powders were acid-digested and analysed with ICP-MS for 30 metals and metalloids. The Loggerhead Turtle shells and eggs contents had higher or statistically significantly higher concentrations than Leatherback Turtles, except for strontium - the reason for this is unknown and needs further investigation. The elemental concentrations in contents and shells were the same or lower compared with other studies. The differences in concentrations in the egg contents and eggshells between the two species are likely due to different trophic levels, life histories, migration patterns, age, gender, and growth, as well as differences in pollution sources and the uptake, retention and elimination characteristics of the different elements by the different species. Nile Crocodile eggshell and egg content profiles did not overlap to such an extent that eggshells could be used as a proxy for elemental concentrations in the egg contents. Iron concentrations in the eggshells of the crocodiles were high. There was also a significant thickening (30%) of the inner shell with increasing iron concentrations. The thicker inner shell could act as a barrier for gas and water exchange. The thicker eggshell may possibly increase the effort needed to break through the eggshell by the emerging hatchling. I found no congruence between patterns (relative elemental contributions) in egg contents and corresponding shells for the three species. However, relative elemental contribution patterns of shells and egg contents showed congruence between the marine turtle species. The lack of congruence between eggshells and contents precludes using eggshells as a proxy for concentrations in egg contents. There was no congruence of profiles when relative elemental contribution patterns of shells and egg contents from freshwater and marine species were compared. Copper concentrations in egg contents were higher than the suggested avian toxic reverence value (TRV) for all three species. The TRV for selenium in the Loggerhead Turtles and Nile Crocodile egg contents were also exceeded. Mercury concentrations were lower than the avian TRV for all three species, but mercury, selenium and copper (at the very least) should be more often monitored in large African reptiles. More research on the effects of pollutants on reptiles in general is needed, especially in the light of possibly strengthened and thicker eggshells of the Nile Crocodile. The hatching success of crocodiles in the KNP is currently unknown and will aid in the evaluation of the effects of iron on the emerging hatchling. The rivers originating outside the KNP were identified as a probable vector of pollution that contributes to greater elemental concentrations in crocodile eggs. Analyses of POPs as well as possible deme discrimination based on compositional pattern differences will aid in marine turtle ecotoxicological research. Turtles were identified as ?active samplers‘ returning to the same location to breed—something that is not practical with marine mammals or elasmobranchs. Here, I present the first reports on metallic elements in marine turtle eggs for the entire Indian Ocean, the first report on the same for crocodile eggs from South Africa, and only the second for crocodiles from Africa, greatly extending the ecotoxicological knowledge of the largest predator in Africa (the Nile Crocodile) as well as the three largest reptiles that breed in Africa.