385-388 Lind

In the past, the Baltic became seriously contaminated by organochlorines (1). The most dramatic increase occurred in the levels of the 2 major organochlorines, namely dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCB) occurred after 1955 (2). A rapid decrease in concentrations of DDT compounds started during the beginning of the 1970s, whereas concentrations of PCB compounds did not decrease until the late 1970s (3). The annual decrease since the beginning of the 1970s has been 9–12% for DDT-compounds. For PCB, the annual decrease since 1975 has been 4–7% (4). In addition, concentrations of dioxins have decreased in the Baltic over the last three decades, although slightly less than the concentrations of PCBs (5). During the 20th century the 3 Baltic seal species, the ringed seal (Phoca hispida botnica), the harbor seal (Phoca vitulina) and the grey seal (Halichoerus grypus) have decreased in number (6). At the beginning of the 20th century the Baltic grey seal population was estimated to include 88 000–100 000 individuals, while, by 1980, the estimated number was not more than 750 (7). After the mid-1950s the decrease is mainly believed to be related to organochlorine pollution of the Baltic and poor reproduction (Härkönen, pers. comm.). High frequencies of uterine stenoses and occlusions among Baltic ringed and grey seals, correlated with high concentrations of DDT and PCB, were reported in the 1970s (8). Further studies in Baltic grey and ringed seals (9, 10) revealed a high frequency of uterine leiomyoma in grey seals and a disease complex in both species, comprising severe chronic lesions of claws, arterial walls, large intestine, adrenals, (9–11), and kidneys (9, 12). Lesions of skull bones are part of the disease complex and are most evident in Baltic grey seals. These lesions include loss of alveolar bone, widening of teeth sockets, porosity, and frequent severe erosions and perforations of masticatory bones, resembling severe periodontitis (11). Skull bone lesions were found in old as well as in fairly young adult animals of both sexes (11). Also skull asymmetry was observed (13). Accordingly, results from a study on harbor seal skulls from the Swedish west coast and Danish and Swedish waters of the southern Baltic, collected 1835–1988, indicated an influence by environmental pollutants (14). Lesions in harbor seals of the same character as in Baltic grey seals have increased in prevalence during the late 20th century (14). Skeletal lesions and malformations, which might be linked to environmental pollutants, have also been reported in other wild mammalian and nonmammalian species (15–17) as well as in experimental animals (18–23) and in humans (24, 25). Mandibular and maxillar lesions in mink given 3,3',4,4',5-pentachlorobiphenyl (PCB126) or 2,3,7,8-tetrachlorobibenzo-p-dioxin (TCDD) (22, 23) resemble those reported for marine mammals, Baltic seals (11–14) and Beluga whale (16). The aim of the present study was to compare mineral density in mandibular and radius bones of male Baltic grey seals from various time periods by using noninvasive peripheral quantitative computed tomography (pQCT).