Testing the Underlying Chemical Principles of the Biotic Ligand Model (BLM) to Marine Copper Systems: Measuring Copper Speciation Using Fluorescence Quenching.

Speciation of copper in marine systems strongly influences the ability of copper to cause toxicity. Natural organic matter (NOM) contains many binding sites which provides a protective effect on copper toxicity. The purpose of this study was to characterize copper binding with NOM using fluorescence quenching techniques. Fluorescence quenching of NOM with copper was performed on nine sea water samples. The resulting stability constants and binding capacities were consistent with literature values of marine NOM, showing strong binding with [Formula: see text] values from 7.64 to 10.2 and binding capacities ranging from 15 to 3110 nmol mg [Formula: see text] Free copper concentrations estimated at total dissolved copper concentrations corresponding to previously published rotifer effect concentrations, in the same nine samples, were statistically the same as the range of free copper calculated for the effect concentration in NOM-free artificial seawater. These data confirms the applicability of fluorescence spectroscopy techniques for NOM and copper speciation characterization in sea water and demonstrates that such measured speciation is consistent with the chemical principles underlying the biotic ligand model approach for bioavailability-based metals risk assessment.

Fate of anthropogenic cyclic volatile methylsiloxanes in a wastewater treatment plant.

The fate of cyclic volatile methylsiloxanes (cVMS) - octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) - was evaluated in a typical secondary activated sludge wastewater treatment plant (WWTP). Water samples (influent, primary effluent, and final effluent) and sludge (primary sludge and waste activated sludge) samples were collected at overnight low, morning high, afternoon low, and evening high flows. Concentrations of cVMS in influents fluctuated with the influent flows, ranging from 0.166 to 1.13 µg L(-1), 3.47-19.3 µg L(-1), and 0.446-3.87 µg L(-1) for D4, D5, and D6, respectively. Mass balance analysis of cVMS showed the average mass of D4, D5, and D6 entering and exiting the plant in influent and effluent, respectively, were 109 g d(-1), 2050 g d(-1), 280 g d(-1), and 1.41 g d(-1), 27.0 g d(-1), 1.90 g d(-1). The total removal efficiency of cVMS was >96%. To elucidate their detailed removal mechanisms, Mackay's fugacity-based treatment plant model was used to simulate the fate of cVMS through the WWTP. Due to the unusual combination of high hydrophobicity and volatility of cVMS, volatilization in the aeration tank and adsorption to sludge were the two main pathways of cVMS removal from water in this WWTP based on the experimental and modeled results. The morning and evening high influent mass flows contributed almost equally at approximately 40% of the total daily cVMS mass, with D5 accounting for the majority of this daily loading.

Influence of salinity and dissolved organic carbon on acute Cu toxicity to the rotifer Brachionus plicatilis.

Acute copper (Cu) toxicity tests (48-h LC50) using the euryhaline rotifer Brachionus plicatilis were performed to assess the effects of salinity (3, 16, 30 ppt) and dissolved organic carbon (DOC, ∼ 1.1, ∼ 3.1, ∼ 4.9, ∼ 13.6 mg C L(-1)) on Cu bioavailability. Total Cu was measured using anodic stripping voltammetry, and free Cu(2+) was measured using ion-selective electrodes. There was a protective effect of salinity observed in all but the highest DOC concentrations; at all other DOC concentrations the LC50 value was significantly higher at 30 ppt than at 3 ppt. At all salinities, DOC complexation significantly reduced Cu toxicity. At higher concentrations of DOC the protective effect increased, but the increase was less than expected from a linear extrapolation of the trend observed at lower concentrations, and the deviation from linearity was greatest at the highest salinity. Light-scattering data indicated that salt induced colloid formation of DOC could be occurring under these conditions, thereby decreasing the number of available reactive sites to complex Cu. When measurements of free Cu across DOC concentrations at each individual salinity were compared, values were very similar, even though the total Cu LC50 values and DOC concentrations varied considerably. Furthermore, measured free Cu values and predicted model values were comparable, highlighting the important link between the concentration of bioavailable free Cu and Cu toxicity.

Concentrations of cyclic volatile methylsiloxanes in biosolid amended soil, influent, effluent, receiving water, and sediment of wastewater treatment plants in Canada.

A comprehensive surveillance program was conducted to determine the occurrence of three cyclic volatile methylsiloxanes (cVMS) octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) in environmental compartments impacted by wastewater effluent discharges. Eleven wastewater treatment plants (WWTPs), representative of those found in Southern Ontario and Southern Quebec, Canada, were investigated to determine levels of cVMS in their influents and effluents. In addition, receiving water and sediment impacted by WWTP effluents, and biosolid-amended soil from agricultural fields were also analyzed for a preliminary evaluation of the environmental exposure of cVMS in media impacted by wastewater effluent and solids. A newly-developed large volume injection (septumless head adapter and cooled injection system) gas chromatography - mass spectrometry method was used to avoid contamination originating from instrumental analysis. Concentrations of D4, D5, and D6 in influents to the 11 WWTPs were in the range 0.282-6.69µgL(-1), 7.75-135µgL(-1), and 1.53-26.9µgL(-1), respectively. In general, wastewater treatment showed cVMS removal rates of greater than 92%, regardless of treatment type. The D4, D5, and D6 concentration ranges in effluent were <0.009-0.045µgL(-1), <0.027-1.56µgL(-1), and <0.022-0.093µgL(-1), respectively. The concentrations in receiving water influenced by effluent, were lower compared to those in effluent in most cases, with the ranges <0.009-0.023µgL(-1), <0.027-1.48µgL(-1), and <0.022-0.151µgL(-1) for D4, D5, and D6, respectively. Sediment concentrations ranged from <0.003-0.049µgg(-1)dw, 0.011-5.84µgg(-1)dw, and 0.004-0.371µgg(-1)dw for D4, D5, and D6, respectively. The concentrations in biosolid-amended soil, having values of <0.008-0.017µgg(-1)dw, <0.007-0.221µgg(-1)dw, and <0.009-0.711µgg(-1)dw for D4, D5, and D6, respectively, were lower than those in sediment impacted by wastewater effluent in most cases. In comparison with the no-observed-effected concentrations (NOEC) and IC50 (concentration that causes 50% inhibition of the response) values, the potential risks to aquatic, sediment-dwelling, and terrestrial organisms from these reported concentrations are low.

Determination of cyclic volatile methylsiloxanes in water, sediment, soil, biota, and biosolid using large-volume injection-gas chromatography-mass spectrometry.

Several methods were developed to detect the cyclic volatile methylsiloxanes (cVMSs) including octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) in water, sediment, soil, biota, and biosolid samples. Analytical techniques employed to optimize measurement of this compound class in various matrices included membrane-assisted solvent extraction in water, liquid-solid extraction for sediment, soil, biota, and biosolid samples. A subsequent analysis of the extract was conducted by large-volume injection-gas chromatography-mass spectrometry (LVI-GC-MS). These methods employed no evaporative techniques to avoid potential losses and contamination of the volatile siloxanes. To compensate for the inability to improve detection limits by concentrating final sample extract volumes we used a LVI-GC-MS. Contamination during analysis was minimized by using a septumless GC configuration to avoid cVMS's associated with septum bleed. These methods performed well achieving good linearity, low limits of detection, good precision, recovery, and a wide dynamic range. In addition, stability of cVMS in water and sediment was assessed under various storage conditions. D4 and D5 in Type-I (Milli-Q) water stored at 4°C were stable within 29d; however, significant depletion of D6 (60-70%) occurred only after 3d. Whereas cVMS in sewage influent and effluent were stable at 4°C within 21d. cVMS in sediment sealed in amber glass jars at -20°C and in pentane extracts in vials at -15°C were stable during 1month under both storage conditions.