Mussels drive polychlorinated biphenyl (PCB) biomagnification in a coastal food web.

Despite international regulation, polychlorinated biphenyls (PCBs) are routinely detected at levels threatening human and environmental health. While previous research has emphasized trophic transfer as the principle pathway for PCB accumulation, our study reveals the critical role that non-trophic interactions can play in controlling PCB bioavailability and biomagnification. In a 5-month field experiment manipulating saltmarsh macro-invertebrates, we show that suspension-feeding mussels increase concentrations of total PCBs and toxic dioxin-like coplanars by 11- and 7.5-fold in sediment and 10.5- and 9-fold in cordgrass-grazing crabs relative to no-mussel controls, but do not affect PCB bioaccumulation in algae-grazing crabs. PCB homolog composition and corroborative dietary analyses demonstrate that mussels, as ecosystem engineers, amplify sediment contamination and PCB exposure for this burrowing marsh crab through non-trophic mechanisms. We conclude that these ecosystem engineering activities and other non-trophic interactions may have cascading effects on trophic biomagnification pathways, and therefore exert strong bottom-up control on PCB biomagnification up this coastal food web.

Oxygenated fuel induced cosolvent effects on the dissolution of polynuclear aromatic hydrocarbons from contaminated soil.

The cosolvent-induced dissolution of polynuclear aromatic hydrocarbons (PAHs) from contaminated soil caused by oxygenated fuel spills was studied. Oxygenated fuel induces a solvent flushing effect on the contaminated soil due to the high content of oxygenated compounds (i.e., methanol, ethanol, and methyl tert butyl ether (MTBE)). The miscible displacement techniques were applied to evaluate the increased potential for secondary contamination in an impacted site. Significant solubility enhancement of the 18 PAHs monitored during fuel spill simulation and cosolvent flushing is clearly evident when compared to normal water dissolution. The breakthrough concentration profile for each PAH constituent was integrated over the cumulative effluent volume (i.e., the zeroth moment) to determine the total PAH mass removed during the experiment. The removal efficiency of PAHs ranges from 46.6% to 99.9% in three oxygenated fuels (i.e., M85, E85, and oxygenated gasoline) during the fuel spill. Several factors including hydrophobicity of compounds, nonequilibrium dissolution due to nonuniform coal tar distribution, and heterogeneous media properties affect the oxygenated compound-induced dissolution process. This study provides a basis to predict the facilitated transport of hydrophobic organic compounds from subsurface environment due to the cosolvent effects of oxygenated fuels.

An exploratory approach to modeling explosive compound persistence and flux using dissolution kinetics.

Recent advances in the description of aqueous dissolution rates for explosive compounds enhance the ability to describe these compounds as a contaminant source term and to model the behavior of these compounds in a field environment. The objective of this study is to make predictions concerning the persistence of 2,4,6-trinitrotoluene (TNT) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in solid form both as individual explosive compounds and components of octol, and the resultant concentrations of explosives in water as a result of dissolution using three exploratory modeling approaches. The selection of dissolution model and rate greatly affect not only the predicted persistence of explosive compound sources but also their resulting concentrations in solution. This study identifies the wide range in possible predictions using existing information and these modeling approaches to highlight the need for further research to ensure that risk assessment, remediation and predicted fate and transport are appropriately presented and interpreted.

The relationship between disinfection by-product formation and structural characteristics of humic substances in chloramination.

The influence of structural characteristics of humic substances on disinfection by-product (DBP) formation was investigated for seven humic substances isolated from aquatic and terrestrial sources. The structural characterizations included 13C nuclear magnetic resonance (13C NMR) spectroscopy and ultraviolet (UV) spectroscopy. The aqueous humic substances were chloraminated at pH 7.0 and 8.5, with and without the presence of the bromide ion, and analyzed for total organic halogen (TOX), trihalomethanes (THMs), and haloacetic acids (HAAs). Aromatic contents determined by 13C NMR and differential UV absorbance at 254 nm statistically correlated with TOX formation for the humic substances investigated at p < 0.08. In contrast, a lack of correlation was observed for THM and HAA formation and these parameters. This paper also compiles relevant literature and discusses the contrasting reaction response of DBP precursor material to chlorination and chloramination.

Selected resin acids in effluent and receiving waters derived from a bleached and unbleached kraft pulp and paper mill.

Water samples were collected on three dates at 24 sites influenced by effluent from Georgia-Pacific's Palatka Pulp and Paper Mill Operation, a bleached and unbleached kraft mill near Palatka, Florida, USA. The sampling sites were located within the mill retention ponds, Rice Creek, and the St. John's River. Samples were analyzed by gas chromatography-mass spectrometry for abietic, dehydroabietic, and isopimaric acids, all of which are potentially toxic by-products of pulp production. Isopimaric acid concentrations greater than 12 mg/L were measured at the mill's effluent outfall but were less than 20 microg/L at the end of Rice Creek. This result indicates that the waters of Rice Creek provide dilution or conditions conducive for degradation or sorption of these compounds. Large differences in resin acid concentrations were observed between sampling events. In two sampling events, the maximum observed concentrations were less than 2 mg/L for each analyte. In a third sampling event, all of the compounds were detected at concentrations greater than 10 mg/L. Data from the three sample dates showed that resin acid concentrations were below 20 microg/L before the confluence of Rice Creek and the St. John's River in all cases.

Dissolution rates of three high explosive compounds: TNT, RDX, and HMX.

Incidental exposure to high explosive compounds can cause subtle health effects to which a population could be more susceptible than injury by detonation. Proper source characterization is a key requirement in the conduct of risk assessments. For nonvolatile solid explosives, dissolution is one of the primary mechanisms that controls fate and transport, resulting in exposure to these compounds remote from their source. To date, information describing dissolution rates of high explosives has been sparse. The objective of this study was to determine the dissolution rates of three high explosive compounds, 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), in dilute aqueous solutions as a function of temperature, surface area, and energy input. To determine each variable's impact on dissolution rate, experiments were performed where one variable was changed while the other two were held constant. TNT demonstrated the fastest dissolution rate followed by HMX and then RDX. Dissolution rate correlation equations were developed for each explosive compound incorporating the three aforementioned variables, independently, and collectively in one correlation equation.