Tara Shukla

Mercury and other metals in eggs and feathers of glaucous-winged gulls ( Larus glaucescens ) in the Aleutians

Levels of mercury and other contaminants should be lower in birds nesting on isolated oceanic islands and at high latitudes without any local or regional sources of contamination, compared to more urban and industrialized temperate regions. We examined concentrations of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in the eggs, and the feathers of fledgling and adult glaucous-winged gulls (Larus glaucescens) nesting in breeding colonies on Adak, Amchitka, and Kiska Islands in the Aleutian Chain of Alaska in the Bering Sea/North Pacific. We tested the following null hypotheses: 1) There were no differences in metal levels among eggs and feathers of adult and fledgling glaucous-winged gulls, 2) There were no differences in metal levels among gulls nesting near the three underground nuclear test sites (Long Shot 1965, Milrow 1969, Cannikin 1971) on Amchitka, 3) There were no differences in metal levels among the three islands, and 4) There were no gender-related differences in metal levels. All four null hypotheses were rejected at the 0.05 level, although there were few differences among the three test sites on Amchitka. Eggs had the lowest levels of cadmium, lead, and mercury, and the feathers of adults had the lowest levels of selenium. Comparing only adults and fledglings, adults had higher levels of cadmium, chromium, lead and mercury, and fledglings had higher levels of arsenic, manganese and selenium. There were few consistent interisland differences, although levels were generally lower for eggs and feathers from gulls on Amchitka compared to the other islands. Arsenic was higher in both adult feathers and eggs from Amchitka compared to Adak, and chromium and lead were higher in adult feathers and eggs from Adak compared to Amchitka. Mercury and arsenic, and chromium and manganese levels were significantly correlated in the feathers of both adult and fledgling gulls. The feathers of males had significantly higher levels of chromium and manganese than did females. The levels of most metals in feathers are below those known to be associated with adverse effects in the gulls or their predators. However, levels of mercury in some gull eggs are within a range suggesting that several eggs should not be eaten in one day by sensitive humans.

Heavy metal and selenium levels in young cattle egrets from nesting colonies in the Northeastern United States, Puerto Rico, and Egypt

Colonially-nesting species of herons and egrets breed mainly in coastal areas, along rivers or near other large bodies of water. Such areas are also preferred for human development, exposing nesting birds to various pollutants. From 1989–1991, the concentrations of heavy metals and selenium were studied in the feathers of fledgling cattle egrets Bubulcus ibis, a terrestrially-feeding insectivore, from New York and Delaware in the northeastern United States, from Puerto Rico, and from Egypt. There were geographic differences in the concentrations of lead, mercury, cadmium, manganese, selenium, and chromium in the feathers of these egrets. Lead levels were 41 times higher in the feathers of cattle egrets from Cairo compared to the other sites. This difference was attributed to the continuing use of leaded gasoline and the dense automobile traffic in Cairo. However, other differences remain unexplained. Similarly, levels of chromium and manganese were also higher in Cairo than at any other sites. Cadmium levels were similar at all places except for higher levels in eastern Puerto Rico. Mercury concentrations were twelve times higher in the feathers of cattle egrets at Aswan compared to Cairo. In Puerto Rico, we also compared levels in adult cattle egrets with young and found higher concentrations of mercury and manganese, but lower concentrations of selenium in the adults. Using feathers from young cattle egrets is a potentially sensitive tool for biomonitoring for metals, especially lead, since they reflect the local area surrounding the breeding colony.

Heavy metals in Pacific cod (Gadus macrocephalus) from the Aleutians: location, age, size, and risk.

Considerable attention has been devoted to the risks from mercury (Hg) and polychlorinated biphenyls (PCB) to high-level predators (including humans) who consume freshwater fish. Although the U.S. Food and Drug Administration (FDA) issued advisories because of Hg for four marine fish species, there are few data on lead (Pb), cadmium (Cd), or other metals in Bering Sea fish generally, or on the risk these levels pose to the fish themselves or to consumers of marine fish. Levels of arsenic (As), Cd, chromium (Cr), Pb, Hg, and selenium (Se) levels were examined in muscle and liver of 142 Pacific Cod (Gadus macrocephalus) collected in 2004 at Nikolski, Adak, Amchitka, and Kiska Islands in the Aleutian Chain (Alaska) in the Bering Sea/North Pacific Ocean, a major source of commercial fishing. One key objective was whether there were location, age, gender, and size effects on tissue concentration that might pose a risk to the fish or their predators (including humans). All fish were measured and weighed, and a subset was aged by examining otolith layers. As was higher in liver than in muscle (geometric mean 2420 versus 1590 ng/g or ppb wet weight), as were Cd (GM 224 versus 1.92) and Se (GM 1380 versus 165). Conversely, Cr was higher in muscle (76.8 versus 45 ppb), as were Pb (23.7 vs 12 ppb) and surprisingly Hg (128 versus 82 ppb). Adak, until recently a large military base, had the highest levels of As, Hg, and Se, while Amchitka had the highest Pb levels, but Nikolski, which generally had the lowest levels, had relatively high Pb in liver. In general, interisland differences were significant for most metals in muscle, but only for Cr in liver. Weight and length were positively related to age, but age tended to explain more of the variance in metal levels. The multiple regression relationships differed by tissue in an unanticipated manner. Location contributed significantly to the models for muscle Cd, Pb, Hg, and Se, but not for liver levels. Conversely the length by weight interaction entered all of the liver models but none of the muscle models. Se and Hg were positively but weakly correlated in both liver (tau = +0.16) and muscle tissue (tau = 0.12). Hg was positively correlated with length, weight, and age in muscle, but not in liver. As showed a significant negative correlation with size variable in both tissues, and Cr was negatively correlated in muscle. Cd was positively correlated with Hg, Se, and As. Between liver and muscle there were significant positive correlations for Hg (tau = .24), As (tau = .407), and Cr (tau = 0.17), but not for Pb, Cd, or Se. In this study, the only metals that might pose a risk to cod-eating predators is Hg, as well as some of the higher values of Pb at Amchitka and Nikolski . The U.S. Environmental Protection Agency (EPA) reference dose (RfD) (not available for lead) was used to evaluate the risk to people consuming an 8-ounce (228g) meal of cod once per day and once per week, and to calculate risk using the levels found in this study. If a subsistence fisher from one of the Aleut villages ate one meal of cod per week for As, or one meal per day for Hg, they would exceed the U.S. EPA reference dose for As and Hg (set at a level to be without adverse effect for any person with this average daily exposure).

Metal levels in horseshoe crabs (Limulus polyphemus) from Maine to Florida

There is considerable concern for the health of spawning populations of horseshoe crabs (Limulus polyphemus) along the east coast of North America because of an increase in the harvest, an apparent decrease in population levels, and the dependence of migrating shorebirds on a superabundant supply of horseshoe crab eggs during their migratory stopover on Delaware Bay. In addition to overfishing, population declines could be caused or recovery slowed, by pollution. In this paper, we examine the levels of metals (arsenic, cadmium, chromium, lead, manganese, mercury, and selenium) in the eggs, leg muscle, and apodeme of 100 horseshoe crabs collected at nine sites from Maine to Florida. Arsenic levels were the highest, followed by manganese and selenium, while levels for the other metals averaged below 100ppb for most tissues. Arsenic and mercury levels were highest in the leg muscle; cadmium, lead, manganese, and selenium levels were highest in eggs; and chromium levels were highest in the apodeme. There were significant geographical differences for all metals in all three tissues. No one geographical site had the highest levels of more than two metals. Arsenic, with the highest levels overall, was highest in Florida in all the three tissues. Manganese levels were highest in Massachusetts for eggs and apodeme, but not leg, which was highest in Port Jefferson, New York. Selenium was highest in apodeme from Florida, and in eggs and leg muscle from Prime Hook, Delaware. The patterns among locations and tissues were not as clear for the other metals because the levels generally averaged below 100ppb. The levels of contaminants found in horseshoe crabs, with the possible exceptions of arsenic in Florida, and mercury from Barnegat Bay and Prime Hook, were below those known to cause adverse effects in the crabs themselves or in organisms that consume them or their eggs. Our results indicate that site-specific data are essential for managers to evaluate the potential threat from contaminants to both the horseshoe crabs and those that consume them.

Effects of color on cadmium and lead levels in avian contour feathers

The use of feathers has been proposed as a noninvasive tissue for biomonitoring metal levels in birds and their ecosystems. We examined cadmium and lead levels in black and white contour feathers from common (Sterna hirundo) and sooty (S. fuscata) terns, and black skimmers (Rynchops niger) to determine if there were significant differences in metal levels related to the melanin content of the feathers. There were no significant differences in metals in black versus white body feathers in any of the three species; correlations between metal residues from individual birds were low.

Metals in feathers of sooty tern, white tern, gray-backed tern, and brown noddy from islands in the North Pacific.

Levels of heavy metals are usuallyhigher in adult than young birds because they eatlarger, more contaminated prey, or because they havehad longer to accumulate metals in their tissues.Further, levels of contaminants are usually less inbirds nesting on remote, offshore islands than inbirds breeding closer to mainland areas that areurbanized and industrialized. We examined the featherlevels of arsenic, cadmium, chromium, lead, manganese,mercury, and selenium in adult sooty terns (Sterna fuscata), gray-backed terns (Sterna lunata), and brown noddy (Anous stolidus, and adult and young white terns (Gygis alba, fromMidway Atoll, and in adult and young sooty terns andadult brown noddy from Manana Island, Hawaii (chicksof other terns were not available). We tested andrejected the null hypotheses that metal levels are notsignificantly different among species, ages, andlocations. Despite their small size, adult white ternshad the highest levels of lead, arsenic and tin. Brownnoddies had the highest levels of cadmium, chromium,manganese, and selenium. Sooty and white terns had thehighest levels of mercury. Sooty tern adults hadsignificantly higher levels of cadmium, mercury, andselenium than young, while young had significantlyhigher levels of arsenic and manganese. White ternadults had significantly higher levels of selenium andtin than young, while young had higher levels ofcadmium and mercury than adults. Except for mercury,there were significant inter-location differenceswithin species in all heavy metals. Contrary toexpectation, where the differences were great, metalsgenerally were higher in the feathers of terns andnoddies from Midway than from Manana.

Lead levels in exposed herring gulls: Differences in the field and laboratory

We compared blood lead levels for herring gull (Larus argentatus) chicks exposed at two days of age in the field and the laboratory. One randomly selected chick in each family of three was injected with lead, the second with a sterile saline solution, and the third was not injected. Field birds were then completely free-living, and were entirely cared for by their parents. Blood was drawn at 35 or 45 days of age for comparison with laboratory-reared chicks. In both the laboratory and the field, blood lead levels were positively related to dose, and concentrations were lower at 45 than at 35 days of age. However, at each dose, the field birds had lower levels than did the laboratory birds. We postulate that this relates to higher overall activity and accelerated bone development in the field, and perhaps to a move varied diet. Wild young gulls were mobile and practiced flight more often than did laboratory-reared gulls. Growth metabolic, and behavioral factors may enhance deposition of lead in the bone, reducing blood lead. Thus, both in ecological risk assessments and in using birds as bioindicators, caution is required in extrapolating from laboratory studies in field conditions.