Arsenic speciation in marine fish and shellfish from American Samoa

We speciated arsenic compounds in marine fish and shellfish from two islands of the United States Territory of American Samoa in the South Pacific, and found that inorganic arsenic occurred as a minor fraction. The proportion of inorganic arsenic was generally far below the levels of prevailing assumptions typically used in human health risk assessments when only total arsenic is analysed. Fish and shellfish were collected from Tutuila and Ofu between May 2001 and March 2002 (n=383 individual specimens, with 117 composites); sites were selected based on habitat type and were representative of those frequented by local fishers. These islands have moderately developed reef fish fisheries among artisanal fishers, are far removed from any industrial or mining sources of arsenic, and presented an opportunity to study arsenic variations in marine biota from un-impacted environments. Target species were from various trophic levels and are among those frequently harvested for human consumption. We found evidence that arsenic concentrated in some marine species, but did not tend to follow classic trophic patterns for biomagnification or bioaccumulation. For the majority of samples, inorganic arsenic was less than 0.5% of total arsenic, with only a few samples in the range of 1-5%, the latter being mollusks which are recognized to have unusually high arsenic levels in general. This work supports the importance of speciation analysis for arsenic, because of the ubiquitous occurrence of arsenic in the environment, and its variable toxicity depending on chemical form.     

A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions

This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing N(E) equilibrium reactions and a set of reactive transport equations of M-N(E) kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.     

Enantiospecific sublethal effects of the antidepressant fluoxetine to a model aquatic vertebrate and invertebrate

Many contaminants are chiral compounds with enantiomers that may differ markedly in environmental fate, bioavailability, and toxicity. Enantiospecific environmental fate and ecotoxicological information are lacking for many chiral contaminants. The primary objective of this investigation included an assessment of potential enantiospecific differences in sublethal standardized and behavioral responses of the model organisms Pimephales promelas (teleost) and Daphnia magna (crustacean) to the widely prescribed chiral antidepressant fluoxetine. Endpoints assessed included D. magna immobilization, reproduction, and grazing rate and P. promelas survival, growth, and feeding rate. S-Fluoxetine was found to be more toxic to sublethal standardized and behavioral endpoints in P. promelas, potentially because its primary active metabolite, S-norfluoxetine, is more potent than the same metabolite of R-fluoxetine in mammals. This was not observed for D. magna responses. This differential enantiospecific response between model organisms may have resulted from closer target homology between mammals and fish than between mammals and crustaceans. P. promelas feeding rate, an ecologically relevant and mode-of-action related response, was the most sensitive endpoint tested for R- and S-fluoxetine with 10% effect concentration (EC10) values (+/-SE) of 16.1 (+/-20.2) and 3.7 (+/-4.6) microg l(-1), respectively. Up to a 9.4-fold difference in toxicity between enantiomers was observed; P. promelas growth EC10s (+/-SE) for R- and S-fluoxetine were 132.9 (+/-21.2) and 14.1 (+/-8.1) microg l(-1), respectively. Such differences in sublethal responses to fluoxetine enantiomers suggest that enantiospecific toxicity and mode-of-action related responses that are ecologically relevant (e.g., feeding rate) should be considered in future ecological hazard and risk assessments for chiral contaminants.     

Models relating individual and population response to contaminants

Even when present at sub‐lethal levels, toxic compounds have an effect on the dynamics of a population, expressed through altered growth and reproduction rates. We explore some of the potential effects of toxicants on populations, using a simple model that considers a generic toxicant and populations of two species, a primary producer, and a consumer living under food‐limited conditions. The toxicant is assumed to affect the consumers only, and it may enter them either directly from the environment or via their food, the latter opening the possibility of biomagnification. The initial response of the consumer to introduction of a toxicant is invariably a decline in its fecundity and density. However, in the longer term, the equilibrium densities of both producer and consumer may increase or decrease, depending on parameter values and ambient toxicant levels. The surprising case of an increased equilibrium in response to the toxicant occurs if, in the absence of toxicant, the consumers held the producers at a very low level, analogous to ‘overfishing’ in fishery studies. If the toxicant enters the consumer via food, multiple, non‐trivial equilibria are possible. The complex, but interpretable, dynamics exhibited by these simple models will be used to guide studies with more realistic models, for whose development this study forms a prelude.     

A Stream–Wetland–Riparian (SWR) index for assessing condition of aquatic ecosystems in small watersheds along the Atlantic slope of the eastern U.S.

As part of a regional study by the Atlantic Slope Consortium (ASC) to develop ecological and socioeconomic indicators of aquatic ecosystem condition, we developed and tested a protocol for rapidly assessing condition of the stream, wetland, and riparian components of freshwater aquatic ecosystems. Aspects of hydrology, vegetation, in-stream and wetland characteristics, and on-site stressors were measured in the field. The resulting metrics were used to develop an index of overall condition, termed the Stream–Wetland–Riparian (SWR) Index. Values of this Index were compared to existing biotic indices and chemical measures, and to a Landscape Index created using satellite-based land cover data and a geographic information system (GIS). Comparisons were made at several levels of spatial aggregation and resolution, from site to small watershed. The SWR Index and associated Landscape Indices were shown to correlate highly with biological indicators of stream condition at the site level and for small contributing areas. The landscape patterns prevalent throughout the entire watershed do not necessarily match the patterns found adjacent to the stream network. We suggest a top-down approach that managers can use to sequentially apply these methods, to first prioritize watersheds based on a relative condition measure provided by the Landscape Index, and then assess condition and diagnose stressors of aquatic resources at the subwatershed and site level.     

Aggregations and offshore movements as indicators of spawning activity of bonefish (Albula vulpes) in The Bahamas

To identify the timing and location of spawning activity for bonefish (Albula spp.) in the Bahamian archipelago, we used an acoustic telemetry array spanning 44?km² of shallow tidal creeks, flats, and adjacent deeper coastal waters near Cape Eleuthera. In two successive years, we surgically implanted transmitters in male and female bonefish (n?=?60) and examined their movement patterns within the array. Eight bonefish surgically implanted with transmitters as part of an earlier study were also tracked. In 2009, the telemetry information was complemented with snorkeling observations, underwater video, and manual tracking of the same acoustically tagged fish, as well as fish (n?=?3) gastrically implanted with continuous transmitters. During a period of 4?C7?days spanning the full and new moons, primarily between October and May, bonefish moved from their typical shallow flats and aggregated at sites in close proximity to the deep water drop-off of the Exuma Sound. Localized movements of the large schools of bonefish (often?>1,000 fish) at these presumptive pre-spawning aggregation sites included brief trips (<8?h) just after sunset until just prior to sunrise to the abyssal wall at the edge of the Exuma Sound (i.e.,?>1,000?m depth). Tagged bonefish detected at these aggregation sites were subsequently detected back in the tidal creeks and coastal flats shortly after new and full moons and remained at these more typical shallow sites (i.e.,?<2?m depth). Although we did not directly observe spawning events, we did observe ventral nudging and porpoising behaviors, which are potentially associated with courtship. Timing of the observed movements and possible courtship behaviors was coincident with periods when gametes were well developed. Collectively, our study provides the first objective evidence suggesting that the aggregation and seasonal migration of bonefish to deep shelf environments during certain moon phases is for spawning.     

Field demonstration of surfactant-enhanced solubilization of DNAPL at Dover Air Force Base, Delaware

This study reports on a surfactant-based flood for tetrachloroethylene (PCE) removal from a control test cell at the Dover National Test Site. The surfactant formulation (sodium dihexyl sulfosuccinate (Aerosol-MA or AMA), isopropanol and calcium chloride) was able to achieve a high concentration of PCE in swollen micelles (supersolubilization) without vertical PCE migration. The hydraulic system included eight screened wells that were operated in both vertical circulation and line drive configurations. After 10 pore volumes of flushing, the overall PCE removal was 68% (65% of which corresponded to the surfactant flooding alone). In addition, the residual PCE saturation was reduced from 0.7% to 0.2%, and the concentration of PCE in the groundwater was reduced from 37-190 mg/L before the flushing to 7.3 mg/L after flooding. Recycling the surfactant solution reduced the required surfactant mass (and thus cost, and waste) by 90%. Close to 80% of the total PCE removal was obtained during the first five pore volumes which were operated in an upward vertical circulation flow scheme. No free oil phase was observed during the test. Further analysis of multilevel sampler data suggests that most of the trapped oil remaining in the cell was likely localized in secluded regions of the aquifer, which helps explain the lower PCE groundwater concentration after remedial activities. In summary, this field study demonstrated the feasibility of surfactant-enhanced remediation to reduce the mass in the source zone and significantly reduce the PCE aqueous concentration and therefore the risk associated with the contaminant plume.     

Prevalence of sustainable and unsustainable use of wild species inferred from the IUCN Red List of Threatened Species

Unsustainable exploitation of wild species represents a serious threat to biodiversity and to the livelihoods of local communities and Indigenous peoples. However, managed, sustainable use has the potential to forestall extinctions, aid recovery, and meet human needs. We analyzed species-level data for 30,923 species from 13 taxonomic groups on the International Union for Conservation of Nature Red List of Threatened Species to investigate patterns of intentional biological resource use. Forty percent of species (10,098 of 25,009 species from 10 data-sufficient taxonomic groups) were used. The main purposes of use were pets, display animals, horticulture, and human consumption. Intentional use is currently contributing to elevated extinction risk for 28–29% of threatened or near threatened (NT) species (2752–2848 of 9753 species). Intentional use also affected 16% of all species used (1597–1631 of 10,098). However, 72% of used species (7291 of 10,098) were least concern, of which nearly half (3469) also had stable or improving population trends. The remainder were not documented as threatened by biological resource use, including at least 172 threatened or NT species with stable or improving populations. About one-third of species that had use documented as a threat had no targeted species management actions to directly address this threat. To improve use-related red-list data, we suggest small amendments to the relevant classification schemes and required supporting documentation. Our findings on the prevalence of sustainable and unsustainable use, and variation across taxa, can inform international policy making, including the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, the Convention on Biological Diversity, and the Convention on International Trade in Endangered Species.     

Deforestation Predicts the Number of Threatened Birds in Insular Southeast Asia

The world's tropical forests are being cleared rapidly, and ecologists claim this is causing a massive loss of species. This claim has its critics. Can we predict extinctions from the extent of deforestation? We mapped the percentage of deforestation on the islands of the Philippines and Indonesia and counted the number of bird species found only on these islands. We then used the species-area relationship to calculate the number of species predicted to become globally extinct following deforestation on these islands. Next, we counted the numbers of insular southeast Asian endemic bird species considered threatened—i.e., those having "a high probability of extinction in the wild in the medium-term future"—in the latest summary Red Data Book. The numbers of extinctions predicted from deforestation and the numbers of species actually threatened are strikingly similar. This suggests we can estimate the size of the extinction crisis in once-forested regions from the extent of deforestation. The numbers of extinctions will be large. Without rapid and effective conservation, many of the species endemic to insular southeast Asia will soon be lost.