Concurrent Exposure Assessments of Atrazine and Metolachlor in the Mainstem, Major Tributaries and Small Streams of the Chesapeake Bay Watershed: Indicators of Ecological Risk

The goals of this study were to: (1) measure atrazine and metolachlor concentrations during both high and low use periods in the Chesapeake Bay's mainstem/major tributaries, smaller tributaries and representative small agricultural streams during 1995 and 1996; (2) compare these exposure data with toxicity benchmarks for each herbicide to predict ecological risk and (3) use in-stream fish community data collected in the streams to provide supportive data for ecological risk characterization. Spatially, atrazine (<0.10–98 g/L) and metolachlor (<0.10–68 g/L) concentrations were highest in the streams, followed by the small tributaries (<0.10–11 g/L atrazine; <0.10–8.6 g/L metolachlor) with the lowest concentration in the mainstem Bay/larger tributaries (<0.10–0.22 g/L atrazine; <0.10–0.24 g/L metolachlor). Temporally, concentrations of both herbicides were greatest in all three types of habitats in the late spring and early summer. Concentrations of atrazine and metolachlor were very low or non-detectable in all habitats sampled from early August to mid-April. Toxicity benchmarks of 20 g/L for atrazine based on an ecological No Observed Effect Concentration (NOEC) for microcosm/mesocosm studies and an acute 10th percentile of 53 g/L for metolachlor (protection of ninety % of the species) based on laboratory toxicity data were selected to assess annual and seasonal ecological risk. Both of these toxicity benchmarks were conservative estimates of ecological risk designed to protect the trophic group (plants) most sensitive to these herbicides. Based on a comparison of these toxicity benchmarks with two years of exposure data, the ecological risk from both atrazine and metolachlor exposure in the mainstem Chesapeake Bay/large tributaries, small tributaries and representative agriculturally dominated streams was generally judged to be low. During one 72-h stream rain event in 1995, the atrazine toxicity benchmark (20 g/L) was exceeded during part of the event. However, long-term permanent ecological effects are not expected based on the documented recovery potential of the most sensitive trophic group (plant communities) to the concentrations of atrazine reported and the transient nature of the atrazine pulses. Fish communities at the stream sites receiving the highest concentrations of both herbicides were judged to be healthy based on an Index of Biotic Integrity (IBI) developed for Maryland's coastal plain.     

Temporal variation in Adélie penguin diet at Béchervaise Island,east Antarctica and its relationship to reproductive performance

Diet, and in particular, food quality and quantity can influence the reproductive performance of marine predators. Also, the diet of specialist predators is often monitored in programmes that model and manage ecosystems. We examined the diet of Adélie penguins (Pygoscelis adeliae), an important consumer of Southern Ocean living resources, at Béchervaise Island, east Antarctica, during the chick-rearing periods for 11 years between 1991–1992 and 2002–2003. We also investigated the relationship between diet and annual reproductive performance. Substantial inter- and intra-annual variation in both meal mass and composition was evident: adults generally returned with larger food loads during the crèche compared with the guard stages, and diet composition was dominated by two prey types, krill and fish, which combined contributed to >90% of the diet by mass in 7 out of 11 years. Females generally brought back meals dominated by krill; males generally consumed fish-dominated meals. However, both sexes returned with a high proportion of krill when annual mean meal mass was also high, suggesting that more food was available in high krill years. There was also evidence that years of high reproductive performance were positively correlated with years of both high meal and krill mass. We believe that our results indicate that there is significant long-term inter- and intra-annual variability in the amount of food available to Adélie penguins and that this was reflected in their diet and measures of reproductive performance. Coupled with the observation that penguins did not switch prey, this indicates that Adélie penguins from Béchervaise Island are dependent predators of krill. This contrasts with populations in other locations but supports the notion that Adélie penguins are an informative species to monitor the management of Southern Ocean marine living resources in this region.     

Geometry of Zn(II) complexes with dissolved organic matter: X-ray studies at variable pH

The structure of Zn(II) complexes with dissolved organic matter (DOM) is an important consideration in developing molecular-level models of Zn(II) speciation, but recent reports favoring the tetrahedral geometry differ from earlier findings that geometry was largely octahedral. In general, the presence of thiolate ligands favors the tetrahedral geometry, while O and N ligands favor the octahedral geometry. This work presents extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopic results, indicating an octahedral geometry over the pH range of 5–9 for a freshwater DOM isolate. Changes in XANES derivatives as a function of pH can be explained in terms of ligand protonation and/or changing ligand groups. Tetrahedral Zn(II)–DOM geometry may be restricted to binding environments containing thiol groups.     

Adsorption and desorption of metolachlor and metolachlor metabolites in vegetated filter strip and cultivated soil

Previous studies have indicated that dissolved-phase metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(methoxy-1-methylethyl) acetamide] transported in surface runoff is retained by vegetative filter strips to a greater degree than either metolachlor oxanilic acid 12-[(2-ethyl-6-methylphenyl) (2-methoxy-1-methylethyl)amino]-2-oxo-acetic acid] (OA) or metolachlor ethanesulfonic acid [2-[(2-ethyl-6-methylphenyl) (2-methoxy-1-methylethyl-1)amino]-2-oxoethanesul-fonic acid] (ESA), two primary metabolites of metolachlor. Adsorption-desorption of ESA and OA in vegetated filter strip soil (VFSS) has not been evaluated, yet these data are required to assess the mobility of these compounds in VFSS. The objective of this experiment was to compare metolachlor, ESA, and OA adsorption and desorption parameters between VFSS and cultivated soil (CS). Adsorption and desorption isotherms were determined using the batch equilibrium procedure. With the exception of a 1.7-fold increase in organic carbon content in the VFSS, the evaluated chemical and physical properties of the soils were similar. Sorption coefficients for metolachlor were 88% higher in VFSS than in CS. In contrast, sorption coefficients for ESA and OA were not different between soils. Relative to metolachlor, sorption coefficients for ESA and OA were at least 79% lower in both soils. Metolachlor desorption coefficients were 59% higher in the VFSS than in the CS. Desorption coefficients for ESA and OA were not different between soils. Relative to metolachlor, desorption coefficients for ESA and OA were at least 66% lower in both soils. These data indicate that the mobility of ESA and OA will be greater than metolachlor in both soils. However, higher organic carbon content in VFSS relative to CS may limit the subsequent transport of metolachlor from the vegetated filter strip.     

Defining Chlorophyll-a Reference Conditions in European Lakes

The concept of “reference conditions” describes the benchmark against which current conditions are compared when assessing the status of water bodies. In this paper we focus on the establishment of reference conditions for European lakes according to a phytoplankton biomass indicator—the concentration of chlorophyll-a. A mostly spatial approach (selection of existing lakes with no or minor human impact) was used to set the reference conditions for chlorophyll-a values, supplemented by historical data, paleolimnological investigations and modelling. The work resulted in definition of reference conditions and the boundary between “high” and “good” status for 15 main lake types and five ecoregions of Europe: Alpine, Atlantic, Central/Baltic, Mediterranean, and Northern. Additionally, empirical models were developed for estimating site-specific reference chlorophyll-a concentrations from a set of potential predictor variables. The results were recently formulated into the EU legislation, marking the first attempt in international water policy to move from chemical quality standards to ecological quality targets.     

Perfluorinated compounds in the Antarctic region: Ocean circulation provides prolonged protection from distant sources

In order to investigate the extent to which Perfluorinated Contaminants (PFCs) have permeated the Southern Ocean food web to date, a range of Antarctic, sub-Antarctic and Antarctic-migratory biota were analysed for key ionic PFCs.Based upon the geographical distribution pattern and ecology of biota with detectable vs. non-detectable PFC burdens, an evaluation of the potential contributory roles of alternative system input pathways is made. Our analytical findings, together with previous reports, reveal only the occasional occurrence of PFCs in migratory biota and vertebrate predators with foraging ranges extending into or north of the Antarctic Circumpolar Current (ACC).Geographical contamination patterns observed correspond most strongly with those expected from delivery via hydrospheric transport as governed by the unique oceanographic features of the Southern Ocean. We suggest that hydrospheric transport will form a slow, but primary, input pathway of PFCs to the Antarctic region.     

Methods of characterizing the distribution of exhaust emissions from light-duty, gasoline-powered motor vehicles in the U.S. fleet

Mobile sources significantly contribute to ambient concentrations of airborne particulate matter (PM). Source apportionment studies for PM10 (PM < or = 10 microm in aerodynamic diameter) and PM2.5 (PM < or = 2.5 microm in aerodynamic diameter) indicate that mobile sources can be responsible for over half of the ambient PM measured in an urban area. Recent source apportionment studies attempted to differentiate between contributions from gasoline and diesel motor vehicle combustion. Several source apportionment studies conducted in the United States suggested that gasoline combustion from mobile sources contributed more to ambient PM than diesel combustion. However, existing emission inventories for the United States indicated that diesels contribute more than gasoline vehicles to ambient PM concentrations. A comprehensive testing program was initiated in the Kansas City metropolitan area to measure PM emissions in the light-duty, gasoline-powered, on-road mobile source fleet to provide data for PM inventory and emissions modeling. The vehicle recruitment design produced a sample that could represent the regional fleet, and by extension, the national fleet. All vehicles were recruited from a stratified sample on the basis of vehicle class (car, truck) and model-year group. The pool of available vehicles was drawn primarily from a sample of vehicle owners designed to represent the selected demographic and geographic characteristics of the Kansas City population. Emissions testing utilized a portable, light-duty chassis dynamometer with vehicles tested using the LA-92 driving cycle, on-board emissions measurement systems, and remote sensing devices. Particulate mass emissions were the focus of the study, with continuous and integrated samples collected. In addition, sample analyses included criteria gases (carbon monoxide, carbon dioxide, nitric oxide/nitrogen dioxide, hydrocarbons), air toxics (speciated volatile organic compounds), and PM constituents (elemental/organic carbon, metals, semi-volatile organic compounds). Results indicated that PM emissions from the in-use fleet varied by up to 3 orders of magnitude, with emissions generally increasing for older model-year vehicles. The study also identified a strong influence of ambient temperature on vehicle PM mass emissions, with rates increasing with decreasing temperatures.