Metals in herring and great black-backed gulls from the New York bight: The role of salt gland in excretion

We examined the tissue distribution of metals in the herring (Larus argentatus) and great black-backed (Larus marinus) gulls obtained near the John F. Kennedy Airport, on Long Island, New York, to determine whether there were species differences and whether levels in the salt gland were sufficiently high to suggest that this organ may be serving an excretory function. For most organs, herring gulls had significantly higher levels of lead (except for liver), but significantly lower levels of mercury (except in the salt gland) than great black-backed gulls. For all metals except arsenic, there were significant differences in concentrations among tissues for both species. Great black-backed gulls had much higher concentrations of cadmium in kidney than in any other organ and this was much higher than the level in herring gulls; herring gulls had much higher levels than black-backs of lead in salt glands. For both species, concentrations in kidney, liver and salt gland were generally higher than in heart muscle or pectoral muscle. For herring gulls, the concentrations of all metals in the salt glands were not significantly different from the organ with the highest values (liver or kidney). For great black-backed gulls this was true only for lead, selenium, chromium, and mercury. We examined the ratio of metals in all organs to the liver concentration. Very low ratios (< 0.25) were found for lead in heart and muscle of both species, and selenium in heart and muscle of herring gulls. High ratios (> 2) included lead (2.75:1) and cadmium (14.3:1) in kidney of black-backs. In great black-backs the kidney:salt gland ratio was > 1.5:1 except for mercury (1.31:1) and chromium (0.83:1), while in herring gulls all ratios were between 0.7 and 1.2, except for mercury (0.46:1), reflecting the relatively higher concentrations of metals in the salt gland of this species. We suggest that most heavy metals seem to be concentrating in the salt glands of gulls, within an order of magnitude of the kidney concentration, and that salt glands may be serving a significant excretory function for these cations.