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Tree swallow (Tachycineta bicolor) eggs and nestlings were collected from 16 sites across the Great Lakes to quantify normal annual variation in total polychlorinated biphenyl (PCB) exposure and to validate the sample size choice in earlier work. A sample size of five eggs or five nestlings per site was adequate to quantify exposure to PCBs in tree swallows given the current exposure levels and variation. There was no difference in PCB exposure in two randomly selected sets of five eggs collected in the same year, but analyzed in different years. Additionally, there was only modest annual variation in exposure, with between 69% (nestlings) and 73% (eggs) of sites having no differences between years. There was a tendency, both statistically and qualitatively, for there to be less exposure in the second year compared to the first year.

The U.S. Army Corps of Engineers conducted a water drawdown on Navigation Pool 8 of the Upper Mississippi River during the summers of 2001 and 2002 to increase aquatic vegetation production and thereby improve fish and wildlife habitat. Flooding of previously dried wetlands, however, may increase the rate of mercury methylation and make mercury more available to terrestrial vertebrates that feed in aquatic environments. Our objective was to determine if mercury, other elements, and organochlorine contaminants were more available to vertebrates following the 2001 drawdown. Tree swallow (Tachycineta bicolor) eggs and nestlings were collected at two sites on Pool 8 and a nearby Reference site in 2000 (pre-2001 drawdown), 2001 (pre-2001 drawdown) and 2002 (post-2001 drawdown) and tissues were analyzed for mercury, other elements, and organochlorine contaminants. Bioindicator measurements of genetic damage, oxidative stress, ethoxyresorufin-O-dealkylase activity, and the ratio of liver to nestling mass were also measured in nestlings at all sites and all years. Based on a multivariate analysis, the 2001 drawdown of Pool 8 did not influence element concentrations, organochlorine concentrations, or bioindicator response. Concentrations of inorganic and organochlorine contaminants in tree swallow eggs and nestlings were not at toxic levels. Hatching success did not differ among years and was comparable to the nationwide average.

Extremely high concentrations of cadmium (3.5 microg/g dry wgt.) and elevated concentrations of chromium (10 microg/g dry wgt.) and mercury (1.6 microg/g dry wgt.) were reported in waterbird tissues at Agassiz National Wildlife Refuge in northwestern Minnesota in 1994. Tree swallows (Tachycineta bicolor) were studied during 1998-2001 at three drainages into the Refuge, two pools on the Refuge, and at a nearby reference location to document whether high levels of contaminants were still present, and if so to quantify the source and severity of the contamination. Trace elements were measured in tree swallow eggs, livers, and diet. Reproductive success and bioindicator responses were monitored. In 2000, water was drawn down on Agassiz Pool, one of the main pools on the Refuge. This presented an opportunity to evaluate the response of trace element concentrations in the diet and tissues of tree swallows after reflooding. High concentrations of trace elements were not detected in swallow tissues, nor were there differences among locations. Less than 20% of swallow samples had detectable concentrations of cadmium or chromium. Mercury concentrations were low and averaged0.25 microg/g dry wgt. in swallow tissues. Trace elements, including mercury, did not increase in tree swallows following the 2000 drawdown at Agassiz Pool. Hatching success and survival of nestlings to 12 days-of-age for tree swallows on the Refuge were similar to the national average and consistent with background trace element concentrations. Bioindicator measurements were within the normal ranges as well.

Within-clutch variability of DDE and PCB residues in eggs from 62 clutches of black-crowned night-herons (Nycticorax nycticorax) was small (12% and 17%) compared to among-clutch variability (88% and 83%). Significant correlations between concentrations of DDE (median r=0.8885) and of PCBs (median r=0.8244) occurred when 501 correlations were run on two randomly selected eggs from within the same clutch; no significant correlation occurred for either concentrations of DDE (median r=0.0353) or PCBs (median r=−0.0843) when eggs were not restricted to the same clutch but were restricted to the same colony. The probability of finding infrequently detected organochlorine contaminants (e.g., DDT, cis-chlordane) in eggs from the same clutch varied from 43–96% and increased as the chemical became more prevalent and the number of eggs per clutch became smaller. These results further support one of the basic assumptions of the sample egg technique, that the chemical residues in one egg in a clutch accurately reflect residues in the remaining eggs of the clutch.

In 2008 and 2009, dredge material from the Mississippi River in Pool 8 south of Brownsville, Minnesota was used to construct nearby islands. Chemical analysis of sediment in 2001 and 2002 in the area to be dredged indicated detectable concentrations of organic and inorganic contaminants. Tree swallows (Tachycineta bicolor), whose diet is mainly aquatic invertebrates, were used to evaluate contaminant exposure in both the dredged and newly created habitat. Organic and inorganic contaminant data were collected from tree swallows in 2007 through 2010 at one study site near the dredging operation, a reference study site upriver from the dredging activity, one study site down river from the dredging activity, and one study site on a newly created island (2009 and 2010 only). Organic and element concentrations were at background levels in all samples. Polychlorinated biphenyl and p,p′-dichlorodiphenyldichloroethylene concentrations in tree swallow nestlings decreased at all study sites over the period 2007 to 2010 including the island study site between 2009 and 2010. Element concentrations in tree swallow livers for the non-island study sites did not show a trend among years in relation to the dredging. Selenium concentrations at the newly created island were higher and cadmium concentrations were lower in 2010 than 2009. Hatching success of eggs in successful nests was not associated with dredging activities.

Our objectives were to measure concentrations of seven trace elements and 14 organochlorine compounds in sediment and biota of the shoalgrass (Halodule wrightii) community of the lower Laguna Madre of south Texas and to determine whether chemicals associated with agriculture (e.g. mercury, arsenic, selenium, organochlorine pesticides) were highest near agricultural drainages. Arsenic, mercury, selenium, lead, cadmium, and organochlorines were generally at background concentrations throughout the lower Laguna Madre. Nickel and chromium concentrations were exceptionally high in shrimp and pinfish (Lagodon rhomboides), which is difficult to explain because of no known anthropogenic sources for these trace elements. For sediment and blue crabs (Callinectes sapidus), mercury was highest near agricultural drainages. Also, DDE was more frequently detected in blue crabs near agricultural drainages than farther away. In contrast, selenium concentrations did not differ among collecting sites and arsenic concentrations were lowest in shoalgrass, blue crabs, and brown shrimp (Penaeus aztecus) near agricultural drainages.

Current and historical point source discharges, storm water runoff, and accidental spills have contaminated the water, sediment, and biota within the Calcasieu Estuary in southwestern Louisiana. In 2003, barn swallow (Hirundo rustica) eggs and nestlings were collected beneath two bridges that cross Bayou d'Inde, the most contaminated waterway within the Calcasieu Estuary. Samples were also collected from a bridge over Bayou Teche, a reference site in south central Louisiana. Polychlorinated biphenyl (PCB) concentrations in barn swallow eggs and nestlings were significantly higher at the downstream site on Bayou d'Inde (2.8 micro g/g PCBs in eggs and 1.5 micro g/g PCBs in nestlings) than at the other two sites (0.2 micro g/g PCBs in eggs and nestlings at both sites). Ethoxyresorufin-O-dealkylase activity in nestling livers was significantly higher at the downstream site on Bayou d'Inde (50 pmol/min/mg) compared to the other two locations (24 pmol/min/mg, each), probably because of exposure to PCBs. Polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran concentrations in eggs and polycyclic aromatic hydrocarbons in nestlings were at background concentrations at all sites. Trace element concentrations in barn swallow eggs and nestling livers were at background levels and did not differ among the three sites. A biomarker of DNA damage did not differ among sites.

Willets (Catoptrophorus semipalmatus) were collected in June and August 1986 at the outlets of two agricultural drainages into the Lower Laguna Madre of South Texas and at two other Texas coastal sites. Mean liver concentration of arsenic was higher in August than June. Over 20% of the livers had arsenic concentrations elevated above a suggested background level of 5.0 ppm dry weight (DW), but concentrations (maximum 15 ppm) were below those associated with acute toxicity. Selenium concentration in livers varied from 2.3 to 8.3 ppm DW for all locations and represented background levels. Mercury concentrations in livers for all locations (means = 2.0 to 3.4, maximum 17 ppm DW) were below those associated with avian mortality and similar to levels found in other estuarine/marine birds. DDE in carcasses was higher in adults (mean = 1.0 ppm wet weight) than juveniles (0.2 ppm), and higher in August (1.0 ppm) than June (0.5 ppm); however, DDE concentrations were generally at background levels. Based on brain cholinesterase activity, willets were not recently exposed to organophosphate pesticides.