Eighty cormorants from the area of Ostroda and Mragowo were used for this study. The analyses were carried out between 1993-1996. Each year 10 two-year-old birds were shot (5 females and 5 males) in two nesting grounds. On average, the amount of concentrated DDT in cormorant liver fat was 4.914 mg/kg and gamma -HCH was 0.039 mg/kg of wet mass. The average amount of DDT in subsequent years varied and ranged from 2.515 to 7.252 mg/kg; however, the differences were statistically insignificant. The females accumulated higher levels of DDT than the males, on average up to 8.796 mg/kg. The differences in DDT amounts concentrated in liver fat of both cormorant groups in different years appeared to be insignificant.

Liver concentrations of gamma -HCH in the observed period most frequently showed tendency to increase, from the level of 0.012 in 1993 to 0.106 mg/kg in 1995. This value decreased in 1996 to 0.003 mg/kg. Higher amounts of gamma -HCH in liver fat were recorded in birds originating form the Mragowo area, excluding the individuals shot in 1995. It was shown that the males accumulated higher levels of gamma -HCH in their livers than the females (years 1993, 1994 and 1996).

The presented study shows the continuous threat of the analyzed xenobiotic agents to water fowl and the need for continuous monitoring of water fowl in respect of their intoxication by DDT and HCH.