Mobilization of arsenic in groundwater of Bangladesh: evidence from an incubation study

The extensive extraction of arsenic (As)-contaminated groundwaters for drinking, household and agricultural purposes represents a serious health concern in many districts of Bangladesh. This laboratory-based incubation study investigated the sources and mechanisms of As mobilization in these groundwaters. Several incubation studies were carried out using sediments collected from the Bangladesh aquifer that were supplemented, or not, with different nutrients, followed by an analysis of the sediment suspensions for pH, ORP (oxidation-reduction potential), EC (electrical conductivity) and As and Fe(ΙΙ) concentrations. In the substrate-amended sediment suspensions incubated under anaerobic environment, there was a mobilization of As (maximum: 50–67 μg/l) and Fe(ΙΙ) (maximum: 182 μg/l), while the ORP value decreased immediately and drastically (as much as −468 mV to −560 mV) within 5–6 days. In the sediment suspensions incubated under control and aerobic conditions, no significant As mobilization occurred. The simultaneous mobilization of As and Fe(ΙΙ) from sediments is a strong indication that their mobilization resulted from the reduction of Fe oxyhydroxide by the enhanced activity of indigenous bacteria present in the sediments; this phenomenon also provides insights on the mobilization mechanism of As in groundwater. The concentrations of As in the sediments used in the incubation studies were strongly linked to the gradients of redox potential development that was stimulated by the quantity of organic nutrient (glucose) used. The penetration of surface-derived organic matter into the shallow aquifer may stimulate the activity of microbial communities, thereby leading to a reduction of iron oxyhydroxide and As release.     

Human impacts, plant invasion, and imperiled plant species in California.

Invasive species are one of the fastest growing conservation problems. These species homogenize the world's flora and fauna, threaten rare and endemic species, and impose large economic costs. Here, we examine the distribution of 834 of the more than 1000 exotic plant taxa that have become established in California, USA. Total species richness increases with net primary productivity; however, the exotic flora is richest in low-lying coastal sites that harbor large numbers of imperiled species, while native diversity is highest in areas with high mean elevation. Weedy and invasive exotics are more tightly linked to the distribution of imperiled species than the overall pool of exotic species. Structural equation modeling suggests that while human activities, such as urbanization and agriculture, facilitate the initial invasion by exotic plants, exotics spread ahead of the front of human development into areas with high numbers of threatened native plants. The range sizes of exotic taxa are an order of magnitude smaller than for comparable native taxa. The current small range size of exotic species implies that California has a significant "invasion debt" that will be paid as exotic plants expand their range and spread throughout the state.     

Effects of ultraviolet radiation and contaminant-related stressors on arctic freshwater ecosystems

Climate change is likely to act as a multiple stressor, leading to cumulative and/or synergistic impacts on aquatic systems. Projected increases in temperature and corresponding alterations in precipitation regimes will enhance contaminant influxes to aquatic systems, and independently increase the susceptibility of aquatic organisms to contaminant exposure and effects. The consequences for the biota will in most cases be additive (cumulative) and multiplicative (synergistic). The overall result will be higher contaminant loads and biomagnification in aquatic ecosystems. Changes in stratospheric ozone and corresponding ultraviolet radiation regimes are also expected to produce cumulative and/or synergistic effects on aquatic ecosystem structure and function. Reduced ice cover is likely to have a much greater effect on underwater UV radiation exposure than the projected levels of stratospheric ozone depletion. A major increase in UV radiation levels will cause enhanced damage to organisms (biomolecular, cellular, and physiological damage, and alterations in species composition). Allocations of energy and resources by aquatic biota to UV radiation protection will increase, probably decreasing trophic-level productivity. Elemental fluxes will increase via photochemical pathways.     

Study of metabolites from the degradation of polycyclic aromatic hydrocarbons (PAHs) by bacterial consortium enriched from mangrove sediments

The PAH metabolites produced during degradation of fluorene, phenanthrene and pyrene by a bacterial consortium enriched from mangrove sediments were analyzed using the on-fiber silylation solid-phase microextraction (SPME) combining with gas chromatography–mass spectrometry (GC–MS) method. Seventeen metabolites at trace levels were identified in different PAH degradation cultures based on the full scan mass spectra. In fluorene degradation cultures, 1-, 2-, 3- and 9-hydroxyfluorene, fluorenone, and phthalic acid were detected. In phenanthrene and pyrene degradation cultures, various common metabolites such as phenanthrene and pyrene dihydrodiols, mono-hydroxy phenanthrene, dihydroxy pyrene, lactone and 4-hydroxyphenanthrene, methyl ester, and phthalic acid were found. The detection of various common and novel metabolites demonstrates that SPME combining with GC–MS is a quick and convenient method for identification as well as monitoring the real time changes of metabolite concentrations throughout the degradation processes. The knowledge of PAH metabolic pathways and kinetics within indigenous bacterial consortium enriched from mangrove sediments contributes to enhance the bioremediation efficiency of PAH in real environment.     

Leaching of atrazine, metolachlor and diuron in the field in relation to their injection depth into a silt loam soil

A field experiment was conducted on a Calcaric Cambisol soil to study the consequences of the penetration depth and properties of pesticides on the risk of subsequent leaching. Three pesticides with different mobility characteristics and bromide were injected at 30 cm (where soil organic matter (OM) was 2%) and 80 cm (soil OM 0.5%) on irrigated plots without a crop. The migration of injected solutes was assessed for two years by sampling the soil solution using six porous cups installed at 50 and 150 cm depth and by relating solute contents to drainage water flux estimated by the STICS model (Simulateur mulTIdisciplinaire pour les Cultures Standard). Pesticides injected at 30 cm were strongly retained so that no metolachlor or diuron was detected at 50 and 150 cm. The ratio of atrazine peak concentration in the soil solution to concentration in the injected solution (C/C₀) was 1 × 10⁻³ and 0.2 × 10⁻³, respectively, at 50 and 150 cm. When injected at 80 cm, (C/C₀) of atrazine, metolachlor and diuron were 10 × 10⁻³, 1 × 10⁻³ and 0.3 × 10⁻³ at 150 cm, respectively; 1/(C/C₀) was correlated with K_oc values reported from databases. The ratio of drainage volume to the amount of water at field capacity in the soil layer between the injection point at 30 cm and the water sampling level (V/V₀) at 50 and 150 cm was 0.6 and 0.9, respectively, for bromide and 1.6 and 1.0 for atrazine. V/V₀ of the injected solutes at 80 cm was for bromide, atrazine, metolachlor and diuron 0.6, 0.9, 1.2 and 1.7, respectively; pesticide V/V₀ was correlated with K_oc. The retardation factor was a good indicator of migration risk, but tended to overestimate retardation of molecules with high K_oc. Atrazine desorption represented an additional leaching risk as a source of prolonged low contamination. The large variability in soil solution of bromide and pesticide concentrations in the horizontal plane was attributed to flow paths and clods in the tilled soil layer. This heterogeneity was assumed to channel water fluxes into restricted areas and thereby increase the risk of groundwater contamination. The methodology used in the field proves to provide consistent results.     

HCHs and DDTs in sediment-dwelling animals from the Yangtze Estuary, China

HCHs and DDTs in sediment-dwelling animals including mollusks and crabs from the Yangtze Estuary were determined by GC-ECD. Levels of t-HCH were in the range of 1.2-5.5 ng g(-1) and averaged 3.5 ng g(-1) in mollusks, while t-DDT concentrations ranged from 26.0 to 68.8 ng g(-1), with a mean of 34.5 ng g(-1). In crabs t-HCH concentrations varied from 2.0 to 25.7 ng g(-1) and averaged 13.8 ng g(-1), whereas the concentrations of t-DDT were in the range of 1.5-24.8 ng g(-1) with a mean value of 5.9 ng g(-1). The HCHs and DDTs levels depend on geographical position and sources, showing the high levels at fresh water area in the estuary, such as XP, CM and LHK sites, and lower at brackish water area, such as FX site, and little difference between species. Results also indicate there was no significant relationship between t-HCH (t-DDT) concentrations and lipid contents both in mollusks and crabs because of non-equilibrium state under a specific estuarine dynamics; smaller individuals accumulated more HCHs and DDTs than larger individuals of mollusks at LHK site, showing different uptake rate for these pesticides; moreover, HCHs and DDTs levels were lower in female crab bodies than male crab bodies suggesting that the release of spawning. BSAFs (Biota- Sediment Accumulation Factors) from sediment-dwelling animals for HCHs and DDTs show a significant "one high with two low" and "one low with two high" effect in the Yangtze Estuary.     

Perfluorinated chemicals in selected residents of the American continent

Perfluorinated chemicals (PFCs) are used in multiple consumer products. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), the most widely studied PFCs, may be potential developmental, reproductive, and systemic toxicants. Although PFCs seem to be ubiquitous contaminants found both in humans and animals, geographic differences may exist in human exposure patterns to PFCs. We measured 11 PFCs in 23 pooled serum samples collected in the United States from 1990 through 2002, and in serum samples collected in 2003 from 44 residents from Trujillo, Peru. PFOS and PFOA were detected in all the pooled samples; perfluorohexane sulfonic acid (PFHxS) was detected in 21. Median concentrations were 31.1 micrograms per liter (mug/l, PFOS), 11.6 microg/l (PFOA), and 2 microg/l (PFHxS). The 90th percentile concentrations of PFCs in the 44 Peruvian residents were 0.7 microg/l (PFOS), 0.1 microg/l (PFOA), and <0.3 microg/l (PFHxS). The frequencies of detection were 20% (PFOS), 25% (PFOA), and 9% (PFHxS). The frequent detection of selected PFCs in the pooled samples from the United States and the lack of clear concentration trends based on a year of collection suggest a sustained widespread exposure to these compounds among US residents, at least since the 1990s. By contrast, the much lower frequency of detection and concentration ranges of PFCs in Peru suggest a lower exposure of Peruvians to PFCs compared with North Americans. Genetic variability, diet, lifestyle, or a combination of all these may contribute to the different patterns of human exposure to PFCs in the United States and Peru.     

Transfer of nutrients and labile metals from the continent to the sea by a small Mediterranean river

The contribution of small watersheds to coastal pollution in Mediterranean areas is still poorly known, and presents great variations along an hydrological year. This work deals with the characterization and quantification of Al, Fe, Zn, Cu, Pb, Si, NO(3)(-) and organic carbon transported from the continent to the sea by a small coastal river in the French Mediterranean area. Transported species were characterized both during rainy and dry periods. During non-rainy periods (base-flow), waters showed a low content of contaminants, whereas during heavy rain events, following dry periods, some metals and organic carbon reached concentrations that could affect biological populations. These contaminants were mainly found in the particulate fraction, originating from the runoff of surface waters, which represents the main process of pollution in urban areas.     

An assessment of the risks associated with polychlorinated biphenyls found in the stomach contents of stranded Indo-Pacific Humpback Dolphins (Sousa chinensis) and Finless Porpoises (Neophocaena phocaenoides) from Hong Kong waters

The risks to Indo-Pacific Humpback Dolphins and Finless Porpoises associated with polychlorinated biphenyls (PCBs) were assessed. Stomach contents from twelve stranded Humpback Dolphins and sixteen stranded Finless Porpoises were collected. Concentrations of total and isomer-specific PCBs in the stomach contents were determined using dual-column gas chromatography equipped with electron capture detectors (GC-ECD). Risks due to the PCBs were assessed in three scenarios, based on total PCBs (summation of 41 PCB congeners), total toxicity equivalency (TEQs) and PCB 118, using the toxicity reference values (TRVs) as the threshold effects benchmarks. The calculated risk quotients (RQs) showed that risks due to PCBs were generally low or negligible. Specifically, RQs from total TEQs and total PCBs for Finless Porpoises are below one, suggesting that PCBs should be a low risk for the Finless Porpoise in Hong Kong waters. However, the Humpback Dolphin has RQs larger than 1 for total TEQs and total PCBs when the 95th percentile data were used in the evaluation. This indicates that further investigation may be needed to examine more closely the potential impact of toxic contaminants in the habitat of the Humpback Dolphin.