Impaired immunity in harbour seals (Phoca vitulina) exposed to bioaccumulated environmental contaminants: review of a long-term feeding study.

Abstract

Mass mortalities among seals and dolphins inhabiting contaminated marine regions have led to speculation about a possible involvement of immunosuppression associated with environmental pollution. To evaluate whether contaminants at ambient environmental levels can affect immune function of seals, we carried out an immunotoxicological study under semifield conditions. Two groups of 1 1 harbour seals (Phoca vitulina) originating from a relatively uncontaminated area were fed herring from either the highly polluted Baltic Sea or the relatively uncontaminated Atlantic Ocean. Changes in immune function were monitored over a 2 1/2-year period. The seals that were fed contaminated Baltic herring developed significantly higher body burdens of potentially immunotoxic organochlorines and displayed impaired immune responses as demonstrated by suppression of natural killer cell activity and specific T-cell responses. During a 2-week fasting experiment performed at the end of the feeding study, mobilization of organochlorines from the blubber did not lead to a strong increase of contaminant levels in the blood, and no enhancement of the existing immunosuppression was observed. These results demonstrate that chronic exposure to environmental contaminants accumulated through the food chain affects immune function in harbour seals, whereas short-term fasting periods, which are normal for seals, do not seem to pose an additional risk. The seals of this study were not exposed perinatally to high levels of environmental chemicals, and body burdens of organochlorines measured near the end of the study were lower than those generally observed in free-ranging seals inhabiting many contaminated regions. Therefore, it may be expected that environmental contaminants adversely affect immune function of free-ranging seals inhabiting contaminated regions at least as seriously as observed in these studies. Environ Health Perspect 1 04(Suppl 4): 823-828 (1996)

The Role of Canine Distemper Virus and Persistent Organic Pollutants in Mortality Patterns of Caspian Seals (Pusa caspica)

“…These actual and predicted TEQ concentrations were compared to ∑TEQ levels observed in experiments with harbour seals [56]. Levels of 196−220 pg/g lipid weight and 58–66 pg/g lipid weight were seen for experimental and control groups of juvenile harbour seals which had been fed contaminated and uncontaminated fish respectively over a 126 week period [1], [56]–[62]. Impaired immune responses were found in the experimental group, and therefore ∑TEQ levels of around 200 pg/g lipid weight were considered to be immunotoxic, although Kannan et al (2000) suggest a threshold of ∼520 pg/g lipid weight for marine mammals.…”

Endocrine Disruption in Wildlife: Background, Effects, and Implications

“…In a two-year feeding experiment, female harbor seals fed fish from the polluted Wadden Sea displayed a lower reproductive success than seals fed less contaminated fish from the Atlantic Ocean [96]. In a second long-term feeding study, it was shown that ambient levels of environmental contaminants, notably PCBs, are immunotoxic to harbor seals [100]. In the same study, implantation failure was found to be associated with lower levels of E2 [99].…”

Persistent Pollution – Past, Present and Future

“…De Swart et al (1994Swart et al ( , 1996 performed a feeding study under semifield conditions with harbour seals consuming herring from areas of different contamination levels. Two groups of eleven harbour seals each were housed in two similar basins over a two and a half year period, so that the same individuals could be repeatedly sampled for monitoring of haematological and immunological parameters in regularly taken blood samples.…”