Recent documentation of sea turtle strandings on Texas beaches has raised questions about the cause for these elevated mortalities. These strandings have also enhanced public concern for the integrity of the coastal environment in the Gulf of Mexico. Since Texas is the site of three major industries - chemical, shrimp, and oil- whose operations are perceived in conflict with the well-being of sea turtle stocks, it is important to determine what role, if any, these industries may have played in the recent increase in sea turtle deaths.

Chemical pollutants introduced either anthropogenically or naturally could affect sea turtles. Petroleum hydrocarbons (oil and its derivatives) are continuously released in large volume by natural seepage from the sea floor, while metals are naturally leached from rocks and minerals on the sea floor. However, it is the site specific release of large amounts of oil, such as the release of oil in Kuwait, the Exxon Valdez spill, or the Megaborg spill, that create major problems and generate the most press coverage. Industrial waste of many kinds frequently contains high concentrations of toxic metals (Hg, As, Pb, Cd), so that dumping or release into the ocean causes focal areas of high concentration. Some heavy metals such as Cu, Se, Fe, and Zn are essential for proper metabolism, but even these elements commonly used in industrial technology can be released in such high concentrations that they become highly toxic.

Organochlorines, for example DDT and its more toxic decomposition compounds, DDD and DDE, are anthropogenic pesticides which have been dumped into the oceans and will continue to remain in the marine environment. These pesticides, as well as numerous others developed in the past and currently being developed by the chemical industry, are major dangers to the marine environment.

The effect of pollutants on sea turtles is difficult to evaluate because the animals are not confined to an easily studied habitat. The size and life span of turtles as well as regulatory restrictions on endangered and threatened species prevents contained laboratory studies of these animals. This paper focuses on measurement of selected heavy metal, organochlorine pesticide, and poly-aromatic hydrocarbon concentrations found in sea turtles stranded on the Texas coast during a specific point in time (July 10 to July 13, 1990).

Four days after the beginning of the Texas Gulf shrimping season (July 6, 1990) 30 endangered sea turtles were found dead within the next four days (July 10 to July 13) along the upper Texas Gulf Coast. Thirteen loggerheads (Caretta caretta) and 17 Kemp's ridleys (Lepidochelys kempi) comprised this standing event. Necropsies were performed on all 30 turtles. Although some were severely autolyzed, liver, kidney, and visceral fat were collected from 20 of the less autolyzed specimens and frozen for toxicological analysis. Prior to the July 10 to July 13 strandings, similar tissues had been collected from 15 stranded turtles (5 loggerheads and 10 Kemp's ridleys). Additional samples were collected from 20 stranded turtles (3 loggerheads and 17 Kemp's ridleys) between July 25 and September 25, a period after the focal time in question.

The objective of this study was to determine if pollutants were elevated in tissue from turtles found dead on the Texas coast between July 10 and July 13. Liver, kidney and visceral fat were analyzed from 10 randomly selected loggerhead turtles (two from the group collected prior to July 10, six from the time period in question, and two from the group collected after July 13). The prior and post turtles were used as controls for the animals found dead between July 10 and July 13. Zinc, Cu, Fe, Cd, Pb, As, and Se were measured by atomic absorption spectroscopy in liver and kidney, while 15 selected organochlorine pesticides and 5 poly aromatic hydrocarbons (PAHs) were measured in visceral fat by organic extraction and gas chromatographic - mass spectroscopic analysis.

Zinc, Fe, Se, Pb, and Cu levels were within ranges previously reported for freshwater turtles, sea turtles, marine mammals, and farm animals. Mercury and As concentrations were within the range reported for many land animals and for bowhead whales, as recently determined in our laboratory (data reported elsewhere). Cadmium levels were elevated when compared to levels reported in other turtle studies, but were within the range reported for whales and dolphins and generally well below levels reported in terrestrial animals with known Cd toxicity. In no case was the metal level in the turtles in question significantly different from turtles that died before or after the July 10 to July 13 date. It is highly unlikely that any of these turtles died as a result of metal toxicity.

No consistent pattern of organochlorine pesticides was found in the turtles tested and the levels found were well below levels considered dangerous in eggs or fish used for human consumption. No PAHs were detected in any tissue. It is clear that these pollutants did not pose a health risk to any of the turtles analyzed.

In conclusion, the pollutants measured were not excessively elevated in any of the tissues for the turtles of this study and there were no differences between groups. These findings, along with the absence of pathological confirmation of toxicity or disease, would seem to rule out pollutant-induced death in these turtles. One must then pay attention to the correlation of the marked elevation of strandings within a few days of the onset of shrimping season.