High levels of cadmium in Atlantic seabirds and sea-skaters

The possibility that cadmium may be an environmental pollutant has caused concern because it has toxic effects on many animal species including man, rat, rabbit, chicken, quail, and pigeon1–4. The occurrence of cadmium in wildlife is not unusual and samples of marine species taken from around the British coast contain low levels (less than 0.5 mg per kg in fish and less than 2 mg per kg in most shellfish); however, levels of up to 93 mg per kg were present in limpets, Patellasp., collected from areas of natural mineralisation or industrial sources of cadmium5. Seabirds generally contain higher residues than marine invertebrates. For example, Anderlini et al.6 examined the amounts of nine metals in the livers of seven Antarctic and Pacific seabird species and noted that the maximum mean cadmium residue occurred in 10 ashy petrels Oceanodroma homochroa collected from their breeding grounds in California (mean residue was 53.2plusminus20.5 mg per kg). Parslow et al.7 found up to 22.3 mg per kg dry wt cadmium in livers of eight puffins Fratercula arctica collected live from various British breeding colonies. It was suggested that pelagic birds might contain higher residues than coastal living species because a single fulmar Fulmarus glacialis examined by them contained 159 mg per kg cadmium. Anderlini et al. concluded that there was a correlation between increased concentration of cadmium in birds and exposure to industrial influences. Parslow et al. did not attempt to explain the residues they found in puffins, but Bourne8 concluded that individual birds were becoming increasingly contaminated through feeding near areas of local pollution around the British coast. It is debatable whether cadmium should be regarded as a pollutant to seabirds. We report here the occurrence of cadmium residues in the tissues of apparently healthy, breeding seabirds which are considerably higher than any previously found. More important, we conclude that the cadmium has a natural rather than an industrial origin, since we have found high cadmium residues in a marine insect, Halobates, which is widely distributed in tropical regions far from sources of industrial cadmium. This insect is only one example of the sources from which birds obtain their cadmium residues.