Regional variation and relationships between the contaminants dde and selenium and stable isotopes in swallows nesting along the Rio Grande and one reference site, Texas, USA

Organochlorine pollutants and stable isotopes in resident and migrant passerine birds from northwest Michoacán, Mexico

Although concentrations of organochlorine compounds (OCs) in birds from most of the United States and Canada have decreased over the last 30 years, there is still concern that migrant birds might be exposed to elevated concentrations of OCs during migration in Latin America. The Lerma-Chapala Basin in west-central Mexico is an important migration corridor and wintering area for many species. The objectives of this study were to assess if resident and migrant birds wintering in western Michoacán, Mexico accumulated elevated concentrations of OCs during fall and spring and to determine if the stable isotopes delta(15)N, delta(13)C, and deltaD could be used to predict burdens and origins of DDE accumulation. Resident and migrant passerine insectivorous birds were collected during fall and spring (2001-2002) in northwest Michoacán, near Chapala Lake, Mexico. The carcasses were analyzed for OCs and tail feathers were analyzed for stable isotopes delta(15)N, delta(13)C, and deltaD. The OCs detected in more than 50% of the samples were: oxychlordane (79%), p,p'-DDE (100%), p,p'-DDT (57%), and total PCBs (100%). p,p'-DDE was the OC detected at the highest concentrations, whereas residues of other OCs were near or below detection limits. Overall, there were no significant differences in concentrations of OCs between seasons or between resident and migrant birds. Concentrations of DDE and oxychlordane were somewhat higher in migrant and resident birds during spring than in fall; however, concentrations were significantly different only for oxychlordane. Two resident birds collected in fall and spring had DDE residues >10 microg/g wet weight in carcass. There were no significant differences in delta(13)C and delta(15)N values among species, between seasons, or between migrant and resident birds. However, deltaD values were clearly different between species and helped differentiate migrant from resident birds. deltaD values also were negatively and significantly correlated with DDE concentrations in carcass. Birds with more depleted deltaD values in feathers tended to have higher DDE concentrations than those with less depleted deltaD values, suggesting a potential latitudinal accumulation of DDE. Overall, our results suggest that during fall and spring, there is not a significant buildup of persistent OCs in migrant and resident passerine insectivorous birds in northwest Michoacán, Mexico.

Cliff swallows Petrochelidon pyrrhonota as bioindicators of environmental mercury, Cache Creek Watershed, California

To evaluate mercury (Hg) and other element exposure in cliff swallows (Petrochelidon pyrrhonota), eggs were collected from 16 sites within the mining-impacted Cache Creek watershed, Colusa, Lake, and Yolo counties, California, USA, in 1997-1998. Nestlings were collected from seven sites in 1998. Geometric mean total Hg (THg) concentrations ranged from 0.013 to 0.208 microg/g wet weight (ww) in cliff swallow eggs and from 0.047 to 0.347 microg/g ww in nestlings. Mercury detected in eggs generally followed the spatial distribution of Hg in the watershed based on proximity to both anthropogenic and natural sources. Mean Hg concentrations in samples of eggs and nestlings collected from sites near Hg sources were up to five and seven times higher, respectively, than in samples from reference sites within the watershed. Concentrations of other detected elements, including aluminum, beryllium, boron, calcium, manganese, strontium, and vanadium, were more frequently elevated at sites near Hg sources. Overall, Hg concentrations in eggs from Cache Creek were lower than those reported in eggs of tree swallows (Tachycineta bicolor) from highly contaminated locations in North America. Total Hg concentrations were lower in all Cache Creek egg samples than adverse effects levels established for other species. Total Hg concentrations in bullfrogs (Rana catesbeiana) and foothill yellow-legged frogs (Rana boylii) collected from 10 of the study sites were both positively correlated with THg concentrations in cliff swallow eggs. Our data suggest that cliff swallows are reliable bioindicators of environmental Hg.

Preliminary environmental monitoring of water quality in the Rio Grande in the Laredo-Nuevo Laredo Region

The international border region of the Rio Grande faces severe environmental and economic challenges. Contamination and degradation of its fragile lotic environments are mainly due to stresses from rapid population growth and unchecked industrial development. This study evaluates the water quality of the Rio Grande in the area of Nuevo Laredo, Mexico and Laredo, Texas, USA, in terms of physical, chemical and bacteriological parameters, as well as total metals, organochlorine pesticides, volatile organic compounds (VOC), semi-volatile organic compounds (SVOC) and radioactivity. Surface water samples were collected at 3 sites along the river. Two additional non-river sites (potable water and residual water) were studied for a better assessment of water quality in the region. Three series of samples were taken every other day during one week (November 3 to November 8, 2005) from the five sampling sites. Levels of oil and grease in all the river samples exceeded the limits established by Mexican regulations. Concentrations of aluminum above the permissible limits for source of drinking water and for quality for protection of freshwater biota were also found in all of the river sites. A number of unregulated elements (Cd, Sr, Mg, Na, Fe, Si, Li and K) appeared in the river samples. The average concentrations of Ba and Na in the potable water samples were below the permissible limits. Ca, Sr, Mg and Si were also found but are not regulated. The majority of the organic compounds studied in both the river and in residual water samples was below detection limits. In all the potable water samples, bromodichloromethane and dibromochloromethane were found above their limit of quantitation (LOQ), but these compounds are not regulated. This preliminary study suggests the need for consistent periodic monitoring to track the environmental status of the Rio Grande.

Residues of toxaphene in insectivorous birds (Petrochelidon spp.) from the Rio Grande, Texas

Although it has been documented that wildlife in the Rio Grande Valley (RGV) contain increased concentrations of organochlorine (OC) contaminants, particularly DDE, little has been published on residues of toxaphene throughout this major North American watershed. In this study, 28 liver composites from adult swallows (Petrochelidon spp.) collected along the Rio Grande from 1999 through 2000 were analyzed for toxaphene residues using congener-specific gas chromatography-electron-capture negative ionization-mass spectrometry. Estimated total toxaphene concentrations ranged from 12 to 260 ng/g wet wt and were highest in samples from the lower RGV near Llano Grande Lake in Hidalgo and Cameron counties (Texas). Toxaphene congener profiles were relatively invariant throughout the watershed and were dominated by 2,2,5-endo,6-exo,8,8,9,10-octachlorobornane (P-42a or B8-806) with lesser amounts of several other Cl(7)-Cl(9) compounds, many of which remain unidentified. Petrochelidon spp. liver profiles appear to be intermediate in complexity between those in invertebrates and fish (more complex) and mammals (less complex) and differs somewhat from those reported for other avian species. In addition to other legacy OC contaminants, toxaphene residues were most concentrated in the lower RGV and accumulated at up to hundreds of parts per billion in these insect-eating birds, underscoring their utility as avian bioindicators of persistent organic pollutants.