In 1988, a significant percentage of seals in the Baltic Sea died from viral diseases; off the coast of Scotland, however, the death rate due to viral diseases was approximately half what it was for the Baltic seals. The Baltic seals had significantly higher levels of pollutants in their blood than did the Scottish seals. Since pollutants are known to impair marine mammals' ability to fight off viral infection, it is likely that the higher death rate among the Baltic seals was due to the higher levels of pollutants in their blood.
The statement 'The kinds of pollutants found in the Baltic Sea are significantly different from those that have been detected in the waters off the coast of Scotland' provides the most additional support for the argument.