Elucidating temporal trends in trace element exposure of green turtles (Chelonia mydas) using the toxicokinetic differences of blood and scute samples

• Published in: The Science of the total environment 2019-02, Vol.651 (Pt 2), p.2450-2459
• Main Authors: Villa, C.A., Bell, I., Madden Hof, C., Limpus, C.J., Gaus, C.
• Format: Article
• Language: English
• Subjects: Animal Scales - chemistry; Animals; Biomonitoring; Blood; Environmental Monitoring - methods; Female; Male; Marine turtle; Scute; Spatio-Temporal Analysis; Tissue Distribution; Toxicokinetic; Toxicokinetics; Trace elements; Trace Elements - blood; Trace Elements - metabolism; Turtles - blood; Turtles - metabolism; Water Pollutants, Chemical - blood; Water Pollutants, Chemical - metabolism
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2018.10.092

Blood is considered a suitable biomonitoring matrix for evaluating relatively recent exposure to environmental contaminants since abrupt changes in exposure regimes are rapidly reflected in blood. On the other hand, keratinized tissues, such as turtle scutes, are known to integrate trace element exposure over relatively long time periods. This study aimed to test the use of the differences in blood and scute to inform on the historical trace element exposure of green turtles. We propose a blood-scute kinetic model to predict how an increase in exposure would affect the concentrations in these two matrices over time. We then tested the relationship between blood and scute concentrations for 19 trace elements in two green turtle populations presumed to experience relatively constant exposure conditions. Significant log-log and linear correlations were observed between blood and scute concentrations for Co, As, Mo, Sb, and Cd. We then analysed blood-scute ratios in turtles from two coastal sites with known elevated exposure to various trace elements from previous studies. Deviations from the steady-state were clearly evident in these coastal turtles (for Co and Cd) and were consistent with the model prediction of changes in exposure. These field data provide evidence that blood-scute ratios can provide a valuable tool for examining the historical trace element exposure of turtles. We further present a method by which the general model may be refined and validated, by using data from individual turtles that had been recaptured across multiple years. Although the timeframe and number of recaptured samples available for this study were limited, the temporal changes in blood-scute ratios in these animals were generally consistent with those suggested by the model. Thus, the ratio between paired blood and scute trace element concentrations could be used to establish a temporal exposure index in turtles. [Display omitted] •A general kinetic model is described for trace elements in turtle blood and scute.•Great Barrier Reef turtles used to approximate steady-state between blood & scute.•Recaptured turtles over successive years provide initial model validation.•Turtles from impacted sites provide case-studies of elevated past exposure to Co.