Quantification of Maternal Offloading of Organic Contaminants in Elasmobranchs Using the Histotrophic Round Stingray (Urobatis halleri) as a Model

Maternal offloading is one route by which young animals may accumulate persistent organic pollutants, such as dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCBs), but has not been well documented in elasmobranchs despite their propensity to accumulate high concentrations of contaminants. Using the round stingray (Urobatis halleri) as a coastal elasmobranch model, we examined maternal offloading processes at two stages in the stingray’s entire reproductive cycle. Post-ovulated and near-term pregnant female stingrays were sampled from southern California, and organic contaminants were measured in the ova and embryonic tissues and compared to concentrations measured in corresponding female livers to determine route and extent of transfer. Total organic contaminant loads measured in ovulated eggs were about two times lower than loads measured in embryos (<i>p</i> < 0.001) indicating mothers have the ability to transfer contaminants throughout pregnancy. Contaminant loads measured in pups showed a positive relationship with mother’s contaminant concentrations (<i>p</i> < 0.001); however, mothers offloaded relatively low percentages (1.5 ± 1.7%) of their total contaminant load using contaminants measured in the liver as a proxy. However, histotrophy is only one form of supplemental provisioning utilized by elasmobranchs and variation in reproductive modes likely influences the extent to which female elasmobranchs may maternally offload contaminants

Map of the study area in the Southern California Bight (SCB).

<p>Black crosses denote the capture location of each individual used in this study. The shaded area represents the Palos Verdes Shelf Superfund Site where large amounts of DDT and PCBs were discharged with effluent and constitute a large portion of the legacy contaminants in the SCB.</p

Parameter values used to simulate dietary bioaccumulation over 365 days.

*<p> = wet weight.</p

Measured concentration of organochlorine contaminants (µg/g, wet weight) in liver of YOY white sharks across total length (TL, cm), compared with maximum expected dietary accumulation over one year.

<p>(A) Dietary accumulation of ΣDDT was estimated to be 25.1±8.23 µg/g (solid and broken reference lines). There was no significant relationship between TL and ΣDDT levels. (B) Dietary accumulation of ΣPCBs was estimated to be 4.73±1.53 µg/g (solid and broken reference lines). There was no significant relationship between TL and ΣPCBs levels.</p

Capture date, total length (TL), percent lipid concentration of the liver and liver concentrations (µg/g, wet weight) for ΣDDT and ΣPCB for the YOY white shark samples.

<p>Capture date, total length (TL), percent lipid concentration of the liver and liver concentrations (µg/g, wet weight) for ΣDDT and ΣPCB for the YOY white shark samples.</p

Observed levels of organochlorine contaminants versus metrics of body condition.

<p>There was no significant relationship between HSI and ΣDDT (A) or ΣPCBs (B). Hepatic lipid levels were positively related to both ΣDDT (C) and ΣPCBs (D).</p