Ecological risk assessment of the effects of neonicotinoid insecticides on northern bobwhites (Colinus virginianus) in the South Texas Plains Ecoregion.

Neonicotinoid insecticides are among the latest class of insecticides that can have harmful effects on birds. Approximately 30 000 kg of neonicotinoid insecticides are applied annually to 429 100 ha of row-crop fields within the South Texas Plains Ecoregion, Texas, USA. Various studies have demonstrated that treated seeds can be highly toxic to northern bobwhites, with the consumption of only 20 corn seeds causing a fatality. Similarly, other studies have indicated that neonicotinoid insecticides can reduce arthropod populations-a substantial prey base for northern bobwhites, especially during the breeding season-by approximately 60%. Our objective was to conduct an ecological risk assessment of neonicotinoid insecticides' impact on northern bobwhite (Colinus virginianus) populations in the South Texas Plains Ecoregion. We estimated that juvenile and adult northern bobwhites could intake from 7.32 to 27.0 mg/kg/day and from 10.0 to 37.5 mg/kg/day of neonicotinoid insecticides, respectively, which can cause adverse effects on growth, reproductive output, and long-term survival. Our study determined that the application of 30 000 kg of neonicotinoid insecticides annually in the South Texas Plains Ecoregion harms the region's northern bobwhite that are exposed to neonicotinoids. Integr Environ Assess Manag 2022;18:488-499. © 2021 SETAC.

The adverse effects of the phenylpyrazole, fipronil, on juvenile white shrimp Litopenaeus setiferus.

Chemical pesticides are commonly used world-wide, and they can flow into estuaries and affect non-targeted organisms. We evaluated the effects of six concentrations of the phenylpyrazole, fipronil (0.0, 0.005, 0.01, 0.1, 1.0, and 3.0 µg/L), which are environmentally relevant, on white shrimp Litopenaeus setiferus (initially averaging 0.80 ± 0.08 g/shrimp). Compared with the control, survivorship of shrimp over 45 days declined significantly at the higher concentration treatments. Growth was affected at all concentrations, and the percent weight gain decreased significantly. Inter-molt intervals were longer in all treatments. Changes in swimming and feeding behavior of shrimp were observed under all treatments, and change in body color was observed at higher concentration treatments. Lipid content in shrimp decreased significantly while ash content increased with fipronil concentration. Fipronil adversely affected white shrimp under the concentrations observed in the environment and monitoring of fipronil use is needed in coastal areas.

Metals and Metalloids in Feathers of Neotropic Cormorants (Phalacrocorax brasilianus) Nesting in Lake Livingston and Richland Creek, Texas, USA.

Breast feathers of Neotropic Cormorants (Phalacrocorax brasilianus) from two nesting colonies in Lake Livingston (LALIV) and Richland Creek, Texas, were collected during 2014 and were analyzed for metals and metalloids. Mean concentrations of Al, As, Cr, Cu, Fe, Pb, Sb, and Se were not significantly different in breast feathers of cormorants from the two locations or between sexes. However, mean concentrations of Co, Mn, Ni, and V were significantly greater in feathers of cormorants from Richland Creek than in those from LALIV; and Zn concentrations were greater in cormorants from LALIV than in those from Richland Creek (p < 0.05). Overall, except for a few outliers for Pb, concentrations of heavy metals and metalloids in feathers were similar or lower than those reported in other species of cormorants from all over the world and were below levels of concern for lethal or sublethal effects on the species.

Persistent organic pollutants in eggs from south Texas Aplomado falcons.

A program to reintroduce the Northern Aplomado falcon (Falco femoralis septentrionalis) in south Texas and the southwestern United States was initiated in the late 1970s. Fledgling Aplomado falcons were first released in the Laguna Atascosa National Wildlife Refuge in 1993 and the first nesting pair in the area was recorded by 1995. During 2004-2017 we collected addled eggs from nesting pairs in the Laguna Atascosa National Wildlife Refuge and Matagorda Island in south Texas, to determine if environmental contaminants in Aplomado falcon eggs had decreased over time and if eggshell thickness values were similar to those in the pre-DDT era. We analyzed organochlorine pesticides, PCBs, and PBDEs in 60 egg homogenates by gas chromatography-mass spectrometry. Eggshells were measured to determine thickness and to correlate with contaminant concentrations. Mean concentration in eggs were 244 ng/g ww for p,p'- DDE, 270 ng/g ww for PCBs and 10 ng/g ww for PBDEs. These values were lower than those reported in a previous study for eggs collected between 1999 and 2003, with a mean of 821 ng/g ww for p,p'-DDE and 1228 ng/g ww for total PCBs. Eggshell thickness ranged from 0.206 mm to 0.320 mm (n = 156). Overall, contaminant concentrations in eggs of Aplomado falcons were low, at levels not likely to impact the recovery of the species. Data from this and previous studies indicate that DDE has decreased significantly in eggs of Aplomado falcons over the last 25 years in south Texas. Breeding populations have been steady at over 30 breeding pairs in south Texas since 2011, although they decreased to 24 pairs in 2018 following Hurricane Harvey.

Effects of insecticides, fipronil and imidacloprid, on the growth, survival, and behavior of brown shrimp Farfantepenaeus aztecus.

Increased use of pesticide is causing detrimental effects on non-target species worldwide. In this study, we examined the lethal and sub-lethal effects of fipronil and imidacloprid, two commonly used insecticides, on juvenile brown shrimp (Farfantepenaeus aztecus), one of the most commercially and ecologically important species in the United States. The effects of six concentrations of fipronil (0.0, 0.005, 0.01, 0.1, 1.0, and 3.0 µg/L) and six concentrations of imidacloprid (0.0, 0.5, 1.0, 15.0, 34.5, 320.0 µg/L) were tested in a laboratory. We examined five different endpoints: growth, moulting interval, survivorship, behavioral change, and body color change. Growth of shrimp was reduced significantly under higher concentrations of both insecticides. Under fipronil exposure, shrimp in control showed the shortest inter-moult interval (7.57 ± 2.17 day) compared with other treatments; similarly, in the imidacloprid experiment, moulting increased from 8.43 ± 2.52 day in control to 11.95 ± 4.9 day in 0.5 µg/L treatment. Higher concentrations of fipronil (1.0 and 3.0 µg/L) showed a 0.0% survival rate compared with 100% survival in the control and 0.005 µg/L treatment. Under imidacloprid, survivorship decreased from 100% in the control to 33.33% in the 320.0 µg/L treatment. The 96-h LC50 of fipronil was 0.12 µg/L, which makes brown shrimp one of the most sensitive invertebrates to the pesticide. Changes in behavior and body color were observed under both insecticides after different durations of exposures depending on concentrations. We conclude that, at the corresponding EPA benchmark concentrations, fipronil had more lethal effects than imidacloprid, and imidacloprid had more sub-lethal effects than fipronil. Both effects are of serious concern, and we suggest monitoring is necessary in estuaries.

Persistent Organic Pollutants in Livers and Hg in Feathers of Neotropic Cormorants (Phalacrocorax brasilianus) from the Trinity River Watershed (Texas, USA).

The Trinity River (Texas, USA) has been historically known as a polluted river because of its proximity to the Dallas-Fort Worth area and because of known discharges of sewage and agricultural irrigation waters to the river. Surprisingly, there are no studies regarding the presence of legacy contaminants in the river and their impacts to wildlife. The objectives of this study were to determine accumulation and potential impacts of persistent organic pollutants, such as organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs), on Neotropic cormorants (Phalacrocorax brasilianus) nesting along the Trinity River. Adult and first-year cormorants were collected from two sites on the Trinity River Watershed during 2014 and 2015. Tissue sections from liver, spleen, kidneys, and gonads were used for histopathology analysis, and a portion of the liver was analyzed for OCPs, PCBs, and PBDEs. Breast feathers were analyzed for Hg. Surprisingly, all the contaminants were present at low concentrations, p,p'-DDE (2-724 ng/g ww), PCBs (28-851 ng/g ww), PBDEs (1-85 ng/g ww), Hg (1.9-3.4 µg/g dw), and below those that could be associated with adverse effects. Also, histological analysis of liver and kidney samples did not reveal morphologic changes consistent with acute or chronic toxicosis. The majority of the histologic changes were inflammatory and were related to parasitic infestation. Our results suggest that aquatic birds using the Trinity River watershed are not at risk for adverse effects due to the contaminants studied. These results should be useful to wildlife managers regarding concerns over contaminant impacts on wildlife of the Trinity River.

Pyocyanin Restricts Social Cheating in Pseudomonas aeruginosa.

Quorum sensing (QS) in Pseudomonas aeruginosa coordinates the expression of virulence factors, such as exoproteases and siderophores, that are public goods utilized by the whole population of bacteria, regardless of whether they invested or not in their production. These public goods can be used by QS defective mutants for growth, and since these mutants do not contribute to public goods production, they are considered social cheaters. Pyocyanin is a phenazine that is a toxic, QS-controlled metabolite produced by P. aeruginosa. It is a redox-active compound and promotes the generation of reactive oxygen species; it also possesses antibacterial properties and increases fitness in competition with other bacterial species. Since QS-deficient individuals are less able to tolerate oxidative stress, we hypothesized that the pyocyanin produced by the wild-type population could promote selection of functional QS systems in this bacterium. Here, we demonstrate, using competition experiments and mathematical models, that, indeed, pyocyanin increases the fitness of the cooperative QS-proficient individuals and restricts the appearance of social cheaters. In addition, we also show that pyocyanin is able to select QS in other bacteria such as Acinetobacter baumannii.

Lethal and sub-lethal effects of the insecticide fipronil on juvenile brown shrimp Farfantepenaeus aztecus.

Chemical pesticides are widely used around the world, but at the same time, they may cause direct or indirect risks to many non-target organisms. Recent increased use of insecticides in coastal areas, for example to control invasive tawny crazy ants, raises concern that insecticides may affect ecologically and/or commercially important species found in estuaries. Here, we investigated the lethal and sub-lethal effects of fipronil on juvenile brown shrimp Farfantepenaeus aztecus over 29 days at five different nominal concentrations (0.1, 1.0, 3.0, 6.4, and 10.0 µg/L) in a laboratory experiment. Exposure to all of the fipronil treatments resulted in all individuals dying before the end of the experiment; whereas, no individual died in the control (0.0 µg/L). The 96-hour LC50 was determined to be 1.3 µg/L. Shrimp also experienced weight loss under all of the fipronil treatments. Inter-moult interval was increased from 12.2 ± 1.64 day in the control group to 15.5 ± 0.53 day in the 1.0 µg/L treatment. Lipid content of shrimp increased significantly in a concentration-dependent manner. Finally, behavioral and body color changes were also observed under the fipronil treatments. We conclude F. aztecus is very sensitive to fipronil and monitoring is needed in coastal areas.

Using Feathers to Evaluate Adverse Effects of Metals on Northern Bobwhites (Colinus virginianus) in Texas.

Northern bobwhites (Colinus virginianus) have been declining across the range of the species primarily due to habitat loss and habitat fragmentation. There is increasing concern regarding effects related to elevated environmental contaminants, including pesticides and metals. Elevated concentrations of some metals are known to have adverse effects on reproduction, development, and survival in birds; however, little research has been conducted on metal exposure in wild bobwhites. We analyzed metal concentrations in the feathers of 60 bobwhites from 3 ecoregions in Texas and evaluated differences between age-class, gender, and location with the objective of determining if bobwhites in Texas are at increased risk of exposure to elevated metal concentrations. We found feather Pb concentrations above the established effect threshold of 4.0 µg/g dry weight at which sublethal and reproductive effects have been reported in birds. More than 25% (n = 16) of the samples analyzed had Pb concentrations above the effect threshold, including four that were five times above the threshold. We also observed slightly elevated feather Cd concentrations, above 0.1 µg/g dry weight, in 17% (n = 11) of the bobwhites analyzed. On average, juvenile bobwhites had higher concentrations of Ba, Co, Fe, Mn, Sr, and V compared to adults (p < 0.05). Additionally, concentrations of Al, Be, Co, Fe, Hg, Ni, Se, Sr, and Tl differed significantly between sampling locations, indicating a potential relationship between metal levels and local agricultural practices. The results of our study indicate a potential risk of sublethal effects of Pb and to a lesser extent Cd in bobwhites in Texas.

Potential impact of neonicotinoid use on Northern bobwhite (Colinus virginianus) in Texas: A historical analysis.

The widespread use of neonicotinoid insecticides in recent years has led to increasing environmental concern, including impacts to avian populations. In Texas and across their range, Northern bobwhite (Colinus virginianus) habitat frequently overlaps cultivated cropland protected by neonicotinoids. To address the effects of neonicotinoid use on bobwhites in Texas, we conducted a historical analysis from 1978-2012 in Texas' ecological regions using quail count data collected from North American Breeding Bird Survey and Texas Parks and Wildlife Department, and neonicotinoid use data from the U.S. Geological Survey. We considered bobwhite abundance, neonicotinoid use, climate, and land-use variables in our analysis. Neonicotinoid use was significantly (p<0.05) negatively associated with bobwhite abundance in the High Plains, Rolling Plains, Gulf Coast Prairies & Marshes, Edwards Plateau, and South Texas Plains ecological regions in the time periods following neonicotinoid introduction (1994-2003) or after their widespread use (2004-2012). Our analyses suggest that the use of neonicotinoid insecticides may negatively affect bobwhite populations in crop-producing regions of Texas.

Estimating coastal wetland gain and losses in Galveston County and Cameron County, Texas, USA.

Coastal wetlands serve many important ecological services. One of these important ecological services is their use as storm buffers. Coastal wetlands provide habitat for migratory birds and aquatic species and can improve water quality. In the late 1990s, the US Fish and Wildlife Service (USFWS) published a study outlining the trends of coastal wetlands from the 1950s to early 1990s. In the present study, wetland gains and losses were calculated for Galveston County and Cameron County, Texas, USA, between 2001 and 2011. Maps from the National Land Cover Database were used to determine wetland areas for the years 2001, 2006, and 2011. ArcGIS was used to compare land cover between the study periods to determine overall wetland losses and gains. A statistical analysis was performed between wetland loss and population data to determine whether increased population density led to a higher loss of wetlands. Our analysis indicates that wetland loss is still occurring, however at a lower rate of loss (0.14%-0.18% annually) than the USFWS study predicted earlier (2.7%). In addition, the majority of wetland losses were due to conversion to upland areas. We found a positive correlation between increased population density and decreased wetland area; however, the trend was not significant. The present study shows how the majority of wetland loss in Galveston and Cameron counties is occurring as a result of increased upland areas. In addition, the present study shows that the use of online mapping systems can be used as a low-cost alternative to assess land changes when field tests are not feasible. Integr Environ Assess Manag 2018;14:120-129. © 2017 SETAC.

Selection of Functional Quorum Sensing Systems by Lysogenic Bacteriophages in Pseudomonas aeruginosa.

Quorum sensing (QS) in Pseudomonas aeruginosa coordinates the expression of virulence factors, some of which are used as public goods. Since their production is a cooperative behavior, it is susceptible to social cheating in which non-cooperative QS deficient mutants use the resources without investing in their production. Nevertheless, functional QS systems are abundant; hence, mechanisms regulating the amount of cheating should exist. Evidence that demonstrates a tight relationship between QS and the susceptibility of bacteria against the attack of lytic phages is increasing; nevertheless, the relationship between temperate phages and QS has been much less explored. Therefore, in this work, we studied the effects of having a functional QS system on the susceptibility to temperate bacteriophages and how this affects the bacterial and phage dynamics. We find that both experimentally and using mathematical models, that the lysogenic bacteriophages D3112 and JBD30 select QS-proficient P. aeruginosa phenotypes as compared to the QS-deficient mutants during competition experiments with mixed strain populations in vitro and in vivo in Galleria mellonella, in spite of the fact that both phages replicate better in the wild-type background. We show that this phenomenon restricts social cheating, and we propose that temperate phages may constitute an important selective pressure toward the conservation of bacterial QS.

Impacts of Heronries on Water Quality as Evaluated through Escherichia coli and Fecal Sterol Analyses.

The authors used fecal sterol analysis to determine the potential contribution of E. coli from heronries to waterbodies in east-central Texas. They analyzed E. coli and fecal sterol concentrations in samples from four heronries during the breeding seasons in 2011-2013. The highest E. coli concentrations were in water samples from the two largest heronries established directly over water. The main sterols in fecal samples were cholesterol and stigmasterol, and in water, cholesterol, coprostanol, and cholestanol. Total sterols ranged 979 to 5838 ng/g dry weight in fecal samples, and 13 to 600 ng/L in water samples. There was a positive correlation between E. coli and the sum of bird sterols in water exposed directly to fecal deposition, but not in water surrounding the heronries. The authors found a strong association between E. coli and stigmasterol, suggesting that the presence of stigmasterol in water could be used for predicting E. coli sources from heronries nesting close to waterbodies.

Estimating the contribution of nitrogen and phosphorus to waterbodies by colonial nesting waterbirds.

Fecal deposition by colonial nesting waterbirds is a potential source of nutrient enrichment and pollution of nearby waterways. Excess concentrations of nitrogen (N) and phosphorus (P) can cause water quality concerns or impairment. We estimated concentrations of N and P deposited to waterbodies by birds nesting in four colonies in east-central Texas during 2011-2013, and developed an age-structured compartment model to estimate the amount of fecal N and P material deposited by birds during the entire breeding season. There was a seasonal variation in the accumulation of N and P in waterbodies where heronries were located with a significant increase from June to July at the peak of the breeding season. Also, there was a significant positive correlation in concentrations of N (P=0.023) in fecal material and water samples from one of the colonies (Murphy Park), suggesting a significant contribution of N from feces to water. Concentrations of N in water near the colonies were also significantly correlated (P=0.004, R2=0.22) with the average amount of precipitation recorded for each region. The simulation model results indicated that total N and P deposition increased proportionally with heronry size, and daily deposition rates varied due to the shifting daily activity budgets of the birds as the breeding season progressed. The total estimated loads from the model reached a maximum of 2170kg N and 240kg P for a given colony, with daily deposition estimated at 22.8kg N, and 2.5kg P. Based on the model, one bird can release about 1mg of N and 0.115mg of P on a daily basis to the soil substrate or directly over water. Results from this study could be useful to estimate the contribution of N and P from wildlife to waterbodies, and for watershed management plans.

Seasonal Differences in Contaminant Accumulation in Neotropical Migrant and Resident Songbirds.

For many years, it has been hypothesized that Neotropical migrants breeding in the United States and Canada accumulate organochlorine pesticides (OCPs) while on their wintering grounds in Latin America. We investigated the seasonal accumulation of persistent organic pollutant (POPs) in migrant and resident passerines in Texas, Yucatán, and Costa Rica collected during the fall, winter, and spring from 2011 to 2013. A total of 153 birds were collected, and all contained detectable levels of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and OCPs with dichlorodiphenyldichloroethylene (DDE) being the most predominant pesticide. OCPs and PCBs were the predominant contaminants, accounting for ≥80 % of the total POPs burden, whereas PBDEs accounted for ≤16 %. Only spring migrants from Texas had significantly greater DDE concentrations (64.6 ng/g dry weight [dw]) than migrants collected in Costa Rica (23.2 ng/g dw). Resident birds in Texas had significantly greater levels of DDE (121 ng/g dw) and ΣPBDEs (34.8 ng/g dw) compared with residents in Yucatán and Costa Rica. For ΣPCBs, resident birds from Costa Rica had significantly lower concentrations (9.60 ng/g dw) compared with their migrant counterparts (43.7 ng/g dw) and residents from Texas (48.3 ng/g dw) and the Yucatán (32.1 ng/g dw). Migrant and resident passerines had similar congener profiles for PCBs and PBDEs suggesting similar exposure and retention of these contaminants. No significant accumulation of DDE was observed in migrants while on their wintering grounds. Relatively high concentrations of PBDEs in resident birds from Costa Rica warrant future studies of PBDE contamination in Latin America.

An Evaluation of the Contribution of Macro- and Microelements from Colonial Nesting Waterbirds to Surface Water.

Macro- and microelements contained in the feces of cattle egrets () and other colonial birds in heronries can be sources of contamination of nearby waterways. Concentrations of the macroelements potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), sulfur (S) and the microelements zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), and boron (B) were measured in water and fecal samples collected from four locations containing heronries during the breeding seasons of 2011, 2012, and 2013. Nitrogen and phosphorus were measured but not reported in this study. Concentrations of K in feces ranged from 8.19 × 10 ± 4.38 × 10 to 4.88 × 10 ± 7.57 × 10 mg kg, and concentrations in water ranged from 3.92 ± 0.05 to 17.93 ± 0.37 mg L. Similarly, concentrations of Ca in feces ranged from 4.17 × 10 ± 1.84 × 10 to 1.16 × 10 ± 4.14 × 10 mg L, and concentrations in water ranged from 25.28 ± 0.89 to 67.88 ± 2.02 mg L. When birds nested directly over water, concentrations of K, Ca, and Mg in water were significantly higher ( < 0.05) than concentrations in water adjacent to birds nesting on islands. The results from this study show that macroelements from avian feces have the potential to enrich surface water and to negatively affect surface water quality. These results provide information regarding the contribution of nutrients from heronries (comprised primarily by cattle egrets) to watersheds.

Effects of captivity and artificial breeding on microbiota in feces of the red-crowned crane (Grus japonensis).

Reintroduction of the threatened red-crowned crane has been unsuccessful. Although gut microbiota correlates with host health, there is little information on gut microbiota of cranes under different conservation strategies. The study examined effects of captivity, artificial breeding and life stage on gut microbiota of red-crown cranes. The gut microbiotas of wild, captive adolescent, captive adult, artificially bred adolescent and artificially bred adult cranes were characterized by next-generation sequencing of 16S rRNA gene amplicons. The gut microbiotas were dominated by three phyla: Firmicutes (62.9%), Proteobacteria (29.9%) and Fusobacteria (9.6%). Bacilli dominated the 'core' community consisting of 198 operational taxonomic units (OTUs). Both captivity and artificial breeding influenced the structures and diversities microbiota of the gut. Especially, wild cranes had distinct compositions of gut microbiota from captive and artificially bred cranes. The greatest alpha diversity was found in captive cranes, while wild cranes had the least. According to the results of ordination analysis, influences of captivity and artificial breeding were greater than that of life stage. Overall, captivity and artificial breeding influenced the gut microbiota, potentially due to changes in diet, vaccination, antibiotics and living conditions. Metagenomics can serve as a supplementary non-invasive screening tool for disease control.

Tracking Metal Pollution in Lake Chapala: Concentrations in Water, Sediments, and Fish.

We measured concentrations of selected metals (Al, Ba, Cu, Mn, Hg, Sr, V, and Zn) in water, sediments, and fish from Lake Chapala and a reference site to evaluate potential negative effects on wildlife, particularly fish-eating birds. Fish metal concentrations ranged from 0.05 µg/g wet weight (ww) for Al and Cu to 64.70 µg/g ww for Sr. There was a positive and significant correlation between fish length and metals particularly for Ba, Cu, Mn, and Zn in Lake Chapala (p < 0.05). However, there were no significant correlations between metal concentrations and δ(15)N values in fish indicating no biomagnification through the food web. Overall, metal concentrations in water, sediments, and fish were similar to and in some cases below those reported for Lake Chapala over the last 20 years. Also, metal concentrations were below those that could be of concern for negative effects on fish and wildlife of Lake Chapala.

Temporal and latitudinal trends of p,p'-DDE in eggs and carcasses of North American birds from 1980 to 2005.

The use of 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT) in agriculture in the United States and Canada was prohibited in the early 1970s; however, it continued to be used restrictively in Mexico until 2000. Forty years later, 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (p,p'-DDE), continues to be detected in eggs and bird carcasses in North America. The use of DDE has been associated with reproductive failure of several avian species, primarily through eggshell thinning. To assess the temporal and latitudinal distribution of p,p'-DDE in North America, the authors examined DDE concentrations reported in bird tissues in the scientific literature published between 1980 and 2009. Overall, the majority of supported models suggested that DDE concentrations in birds were greater in the upper mid-latitudes (38°-48°) than in other parts of North America. However, spatial trends of DDE seemed to be influenced by regions with large amounts of data, such as the Great Lakes area. Concentrations of p,p'-DDE in eggs averaged 2.5 µg/g, 3.2 µg/g, and 29.5 µg/g wet weight in 1980 and decreased to 1.64 µg/g, 0.87 µg/g, and 1.01 µg/g wet weight by the mid-2000s for the central, eastern, and western North America regions, respectively. The results indicate that, over time, all DDE residues observed in birds have decreased significantly in North America. Environ Toxicol Chem 2016;35:1340-1348. © 2016 SETAC.

Accumulation and hazard assessment of mercury to waterbirds at Lake Chapala, Mexico.

Lake Chapala is the largest tropical lake in Mexico. The objectives of this study were to determine bioaccumulation of Hg in fish and to evaluate the potential impacts of Hg in the diet of aquatic birds, particularly the American white pelican (AWPE), in Lake Chapala. Hg concentrations in three fish species ranged from 0.021 to 0.568 µg/g wet weight. Mercury in fish was positively and significantly correlated with total fish length (R2=0.44, P<0.05). The δ15N values in fish were significantly correlated with Hg concentrations in Chapala and the San Antonio Reservoir (R2=0.69, P<0.001 and R2=0.40, P<0.001, respectively). However, Hg concentrations in bird feathers were not significantly different between years, among locations, or among species. Hg concentrations in fish from Lake Chapala were within values reported in many parts of the world. The Hg (mean range of 2.75 to 4.54 µg/g dw) and δD (mean range of -62‰ to -11‰) values in bird feathers suggested a wide pattern of exposure for highly migratory AWPE and egrets, although birds with lower δD values in feathers appeared to have greater concentrations of Hg than those with higher δD values. Contaminant exposure in aquatic birds in Chapala during the breeding season should be monitored next to better determine the potential effects of Hg on resident aquatic birds.