Rapid Cleanup of Chlorinated Solvent Source Zones: Synergies Between Chemical and Biological Degradation

A chlorinated volatile organic compound (cVOC) source area approximately 25 by 100 ft in a heavily industrialized urban area was characterized with groundwater tetrachloroethene (PCE) concentrations up to 9,180 μg/L. This is approximately 6 percent of PCE's aqueous solubility, indicative of the presence of residual dense, nonaqueous phase liquid. The resulting dissolved‐phase plume migrated off‐site. Biotic and abiotic dechlorination using a combination of a food‐grade organic carbon‐based electron donor and zero‐valent iron suspended in a food‐grade emulsifying agent reduced the source area PCE concentrations by 98 percent within 27 weeks, with minimal downgradient migration of daughter products dichloroethene and vinyl chloride. Combining biological dechlorination with iron‐based chemical dechlorination is synergistic, enhancing treatment aggressiveness, balancing pH, and optimizing degradation of both DNAPL and dissolved‐phase cVOCs. © 2013 Wiley Periodicals, Inc.     

Estuarine epifauna recruit despite periodic hypoxia stress

In some estuaries, the recruitment of epifaunal benthic invertebrates coincides with a significant environmental stress, low water-column dissolved oxygen, termed hypoxia (̀ mg O₂ l^-1). Recruitment of epifaunal species was measured in the lower York River, a subestuary of the Chesapeake Bay, USA, which experiences predictable, periodic hypoxia associated with neap/spring tidal cycling during summer. Recruitment substrata were exposed during 48-h deployments in two areas with differing levels of hypoxia, and epifauna were allowed to recruit during periods of low oxygen (neap tides) and high oxygen (spring tides) in 1996 and 1997. Recruitment was often high during neap tides, even when severe oxygen depletion (<0.5 mg O₂ l^-1, <0.71 ml O₂ l^-1) occurred during deployments; indeed, peak recruitment episodes of several dominant epifaunal taxa, and of total epifauna, coincided with hypoxic events during both summers. Increased recruitment during neap tides suggests that factors besides hypoxia influenced recruitment in the York River; these factors may have included changes in larval availability and lower current speeds. This study illustrates how the relationship between recruitment and large-scale stresses, such as hypoxia, may be difficult to predict, since large-scale stresses are often correlated with numerous other factors. Short-term hypoxia appears to have little effect on recruitment in the field for many epifaunal species in this ecosystem, which may explain, in part, why substrata exposed for longer durations (1 month) in this system showed few effects of hypoxia on community composition or diversity. High larval tolerance of hypoxic stress may allow communities to persist even though the summer hypoxia season coincides with the recruitment of many epifaunal species. Electronic Supplementary Material is available if you access this article at http://dx.doi.org/10.1007/s00227-002-0930-6. On that page (frame on the left side), a link takes you directly to the supplementary material.     

ERD of Residual TCE DNAPL Achieving Nondetect from a Single Injection of Food‐Grade Waste

Residual dense nonaqueous phase liquid (DNAPL) composed of trichloroethene (TCE) was identified in a deeper interval of an overburden groundwater system at a manufacturing facility located in northern New England. Site hydrostratigraphy is characterized by two laterally continuous and transmissive zones consisting of fully‐saturated fine sand with silt and clay. The primary DNAPL source was identified as a former dry well with secondary contributions from a proximal aboveground TCE storage tank. A single additive‐injection mobilization in 2001 utilizing a food‐grade injectate formulated with waste dairy product and inactive yeast enhanced residual TCE DNAPL destruction in situ by stimulating biotic reductive dechlorination. The baseline TCE concentration was detected up to 97,400 μg/L in the deeper interval of the overburden groundwater system, and enhanced reductive dechlorination (ERD) achieved >99 percent reduction in TCE concentrations in groundwater over nine years with no evidence of sustained rebound. TCE concentrations have remained nondetect below 2.0 μg/L for the last five consecutive sampling rounds between 2013 and 2015. ERD utilizing a food‐grade injectate is a green remediation technology that has destroyed residual DNAPL at the site and achieved similar results at other residual DNAPL sites during both pilot‐ and full‐scale applications. ©2016 Wiley Periodicals, Inc.     

Differential effects of Aureococcus anophagefferens isolates ("brown tide") in unialgal and mixed suspensions on bivalve feeding

Picoplanktonic brown tides of Aureococcus anophagefferens have had devastating effects on production of commercially exploited bivalve populations in shallow, mid-Atlantic estuaries in the United States. The toxin produced by this alga has not been chemically characterized. This study develops a bioassay using juvenile mussels, Mytilus edulis, based on the inhibitory effect of brown tide on bivalve suspension-feeding, to compare the cellular toxicity of three Long Island, New York, clonal isolates of A. anophagefferens. Two recent (1995) isolates (CCMP 1707 and 1708) from Peconic Bay proved highly toxic and caused greater than 100-fold reduction in clearance rates (CR) of juvenile mussels in unialgal and mixed suspensions with a nutritious alga, Isochrysis galbana (clone T-iso), relative to controls. A third 1986 isolate from Great South Bay (CCMP 1784) showed no detectable toxicity in 24-h trials, and may have lost its initial potency over more than a decade of laboratory culture. Identification of a non-toxic strain provides a useful tool for future research. Cultures of the toxic isolate CCMP 1708 in late-stationary growth phase were significantly more toxic than those in early-exponential phase. The threshold concentration of toxic A. anophagefferens cells that inhibits clearance on co-occurring phytoplankton species was determined for juvenile (10-mm) hard clams, Mercenaria mercenaria. Relatively low concentrations (⣃᎒³ to 50᎒³ cells ml^-1) of isolate CCMP 1708 were sufficient to sharply reduce clam CR of I. galbana. Calculations based on these results suggest that, at peak historical densities of M. mercenaria in Great South Bay, removal of A. anophagefferens at low cell densities by suspension-feeding benthos could provide an effective top-down grazing control mechanism to prevent the initiation of brown tide in shallow, inner bays.     

Modeling non-point source pollution from rice farming in the Thachin River Basin

With the worldwide intensification of agriculture, non-point source pollution of surface waters has become a pressing issue. Conventional river water quality models consider non-point sources as accumulated entries into the rivers and do not investigate into the processes generating the pollution at its source, thus preventing the determination of effective mitigation measures. The models require extensive data inputs, which is a deficiency in many developing and emerging countries with limited data availability. The current study applies a Material Flow Model as a complementary approach to quantify non-point source pollution from agricultural areas. Rice farming in the Thachin River Basin is presented as a case study, with a focus on nutrients. The total nitrogen and phosphorus flows from rice farming to the river system are quantified, the key parameters influencing these flows are determined and potential mitigation measures are discussed. The results show that rice contributes considerable nutrient loads to the Thachin River Basin. Scenario simulations demonstrate that a significant nutrient load reduction could be achieved by following the official recommendations for fertilizer application, thus confirming the local efforts to introduce best management practice. Our results underline the importance of non-point source pollution control in intensive agricultural areas, particularly of tropical lowland delta areas such as the Central Plains of Thailand. The specific benefit of applying a Material Flow Model in this context is that with limited data availability, one can reach an understanding of the system and gain a first overview over its key pollution problems. This can serve as supportive basis for determining consecutive in-depth research requirements.     

Plant invasions, generalist herbivores, and novel defense weapons

One commonly accepted mechanism for biological invasions is that species, after introduction to a new region, leave behind their natural enemies and therefore increase in distribution and abundance. However, which enemies are escaped remains unclear. Escape from specialist invertebrate herbivores has been examined in detail, but despite the profound effects of generalist herbivores in natural communities their potential to control invasive species is poorly understood. We carried out parallel laboratory feeding bioassays with generalist invertebrate herbivores from the native (Europe) and from the introduced (North America) range using native and nonnative tetraploid populations of the invasive spotted knapweed, Centaurea stoebe. We found that the growth of North American generalist herbivores was far lower when feeding on C. stoebe than the growth of European generalists. In contrast, North American and European generalists grew equally well on European and North American tetraploid C. stoebe plants, lending no support for an evolutionary change in resistance of North American tetraploid C. stoebe populations against generalist herbivores. These results suggest that biogeographical differences in the response of generalist herbivores to novel plant species have the potential to affect plant invasions.     

Persistent organic chemicals in sewage effluents: I. Identifications of nonylphenols and nonylphenolethoxylates by glass capillary gas chromatography / mass spectrometry

Nonylphenols and nonylphenolethoxylates with one, two, and three oxyethylene groups were identified in effluents from activated sludge sewage treatment plants. The complex mixtures of isomers are considered to be refractory metabolites of nonionic detergents.     

Hypoxia-induced structural changes in the diet of bottom-feeding fish and Crustacea

Interactive effects of three alternating normoxia-hypoxia cycles on benthic prey exploitation by mobile fish (spot, Leiostomus xanthurus; and hogchoker, Trinectes maculatus) and a burrowing crustacean (Squilla empusa) were investigated in the York River, Chesapeake Bay, Virginia, USA, in 1989. Predators collected in four depth strata (A: 5 to 10 m; B: 10 to 14 m; C: 14 to 20 m; D:>20 m) variously affected by hypoxia were separated into size classes (three for spot and two each for hogchoker and mantis shrimp) to examine potential ontogenetic influences in prey selection. The most severe effects of hypoxia on the benthos occurred in the two deepest strata (C and D) and decreased in shallower strata (B>A), with Stratum A never affected by low oxygen. Predators investigated exhibited dietary evidence of optimal prey exploitation during or immediately after hypoxic events. In most instances gut contents contained significantly larger, deeper-burrowing prey during periods of low oxygen than during alternating peroids of normal oxygen levels. Spot consumed a greater biomass (45 to 73%) of polychaetes than other prey, with crustaceans initially also constituting a main dietary component but decreasing in importance later in the study period. The deep-burrowing anemone, Edwardsia elegans, was an important prey species for spot, particularly in the lower depth strata affected by hypoxia. Prey consumed by 10-to 15-cm-long spot increased significantly in size during some hypoxic events, suggesting a sublethal effect of hypoxia on large benthic species. Polychaetes (primarily Glycera americana, Notomastis latericeus and Loimia medusa) were dominant dietary components in hogchoker, making up between 85 and 98% of the diet. Bivalve siphons became important prey for hogchoker in the three deepest strata and were only consumed after the August hypoxia. Stomach contents of mantis shrimp were difficult to identify in most instances due to the near complete mastication of consumed prey. Crustaceans were important prey initially but became less conspicuous in the diet subsequent to the July hypoxia event, when hydroids became more dominant. Overall, predator species exhibited optimal exploitation of moribund or slowly recovering benthos affected by hypoxia. The sublethal effects of hypoxia through increased availability of benthos to resident predators can have important consequences for energy flow in areas such as the York River which experience periodic low-oxygen cycles.     

Biochemical Treatment of Hydraulically Complex Hexavalent Chromium and Chlorinated Volatile Organic Plumes

Groundwater contaminated with hexavalent chromium (Cr⁺⁶) and chlorinated volatile organic compounds (cVOCs) presents unique in situ remedial challenges in an oxygen‐rich environment. On one hand, chemical oxidation would be effective in treating the cVOCs; however, it would not be appropriate to treat Cr⁺⁶. Biological treatment may be appropriate to treat the Cr⁺⁶; however, the cVOC degradation pathway within these mixed plumes is currently following an abiotic pathway with little to no daughter‐product production. Thus, a blended approach was needed to treat both constituents in situ in an effort to avoid a long‐term, costly pump‐and‐treat solution. This article evaluates an in situ biogeochemical stabilization/reduction strategy by injecting an inorganic carbon‐based remedial additive into the geologic and hydrogeologic environment to decrease concentrations within the commingled Cr⁺⁶ and cVOC plume. The concept involves creating favorable redox reducing conditions to shift the groundwater geochemical equilibrium from the more toxic Cr⁺⁶ to the less toxic trivalent chromium (Cr⁺³), with the final outcome being a conversion to chrome oxide that molecularly fixes to the soil grains. In addition, reducing conditions developed for chromium reduction should result in an increase in the available natural formation iron that should further enhance the natural abiotic reduction of cVOCs. © 2013 Wiley Periodicals, Inc.