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 ofmetals in the herring (Larus argentatus) andgreat black-backed (Larus marinus) gullsobtained near the John F. Kennedy Airport, on LongIsland, New York, to determine whether there werespecies differences and whether levels in the saltgland were sufficiently high to suggest that thisorgan may be serving an excretory function. For mostorgans, herring gulls had significantly higher levelsof lead (except for liver), but significantly lowerlevels of mercury (except in the salt gland) thangreat black-backed gulls. For all metals exceptarsenic, there were significant differences inconcentrations among tissues for both species. Greatblack-backed gulls had much higher concentrations ofcadmium in kidney than in any other organ and this wasmuch higher than the level in herring gulls; herringgulls had much higher levels than black-backs of leadin salt glands. For both species, concentrations inkidney, liver and salt gland were generally higherthan in heart muscle or pectoral muscle. For herringgulls, the concentrations of all metals in the saltglands were not significantly different from the organwith the highest values (liver or kidney). For greatblack-backed gulls this was true only for lead,selenium, chromium, and mercury. We examined theratio of metals in all organs to the liverconcentration. Very low ratios (<0.25) were foundfor lead in heart and muscle of both species, andselenium in heart and muscle of herring gulls. Highratios (>2) included lead (2.75:1) and cadmium(14.3:1) in kidney of black-backs. In greatblack-backs the kidney:salt gland ratio was >1.5:1except for mercury (1.31:1) and chromium (0.83:1),while in herring gulls all ratios were between 0.7 and1.2, except for mercury (0.46:1), reflecting therelatively higher concentrations of metals in the saltgland of this species. We suggest that most heavymetals seem to be concentrating in the salt glands ofgulls, within an order of magnitude of the kidneyconcentration, and that salt glands may be serving asignificant excretory function for these cations.     

Temporal and geographical variations of mercury and selenium in eggs of Larus michahellis and Larus audouinii from central Mediterranean islands

In this study, we determined mercury and selenium levels in abandoned unhatched eggs of the yellow-legged gull (Larus michahellis) and Audouin’s gull (Larus audouinii) collected during 2004–2005 from the Tuscan archipelago and Sardinia (Italy). The different feeding habits of the two species probably determine the different uptakes of trace elements, as the study shows highly significant differences for selenium and mercury levels as well as shell thickness and Hg:Se molar ratio values. Audouin’s gulls nesting on the coasts of the Tuscan archipelago showed significantly higher selenium levels than did gulls from colonies from the islands around Sardinia. Comparisons with a similar investigation previously conducted in the same area suggested that mercury and selenium concentrations, although in line with reports in the literature, were significantly lower than levels encountered in gulls in the early 1980s. Mercury (mg/kg d.w.) dropped from 8.631 to 5.030 in Audouin’s gulls and from 2.509 to 0.828 in yellow-legged gulls. The regional decline in mercury levels following reduced use of the metal in industry and the probable food depletion effects linked to the overfishing of fish prey of these two gull species are discussed as hypotheses that could explain the decrease in mercury levels found in eggs.