Improving tritium exposure reconstructions using accelerator mass spectrometry.

Direct measurement of tritium atoms by accelerator mass spectrometry (AMS) enables rapid low-activity tritium measurements from milligram-sized samples and permits greater ease of sample collection, faster throughput, and increased spatial and/or temporal resolution. Because existing methodologies for quantifying tritium have some significant limitations, the development of tritium AMS has allowed improvements in reconstructing tritium exposure concentrations from environmental measurements and provides an important additional tool in assessing the temporal and spatial distribution of chronic exposure. Tritium exposure reconstructions using AMS were previously demonstrated for a tree growing on known levels of tritiated water and for trees exposed to atmospheric releases of tritiated water vapor. In these analyses, tritium levels were measured from milligram-sized samples with sample preparation times of a few days. Hundreds of samples were analyzed within a few months of sample collection and resulted in the reconstruction of spatial and temporal exposure from tritium releases. Although the current quantification limit of tritium AMS is not adequate to determine natural environmental variations in tritium concentrations, it is expected to be sufficient for studies assessing possible health effects from chronic environmental tritium exposure.

The influence of sediment and colloidal material on the bioavailability of a quaternary ammonium surfactant.

The bioaccumulation and tissue distribution of a quaternary ammonium surfactant (hexadecylpyridinium bromide, HPB) in aquatic organisms was assessed under a variety of exposure conditions. Tadpoles, clams, and minnows were exposed simultaneously to sublethal levels of [3H]HPB under flowthrough conditions for a period of 7 days. Four exposure conditions were studied: water-borne HPB alone, water-borne HPB flowed over a natural sediment, waterborne HPB mixed in a suspension of bentonite clay, and HPB sorbed to a natural sediment. In addition, the significance of ingestion as an exposure pathway for HPB was assessed in a series of oral-dosing experiments conducted with tadpoles. Gill tissues accumulated the highest HPB residues for organisms exposed to the chemical in the absence of sediment or clay. The accumulation of HPB in all tissues, but especially in gills, was reduced significantly in the presence of sediment or clay. This finding is important because gill tissue is a primary site of toxic action for quaternary ammonium compounds. Tadpoles ingested HPB-contaminated sediment and clay, which became a source of exposure for GI-tract tissues. The results of oral-dosing experiments confirmed that sorbed HPB did contribute to the accumulation of this compound in intestinal tissues.

The transfer of trichloroethylene (TCE) from a shower to indoor air: experimental measurements and their implications.

Experiments were performed to measure the transfer of trichloroethylene (TCE), a volatile organic compound (VOC), from tap water in showers to indoor air. In these experiments, the loss of TCE from tap water in the shower is based on the difference between influent and effluent concentrations. We have developed and previously published a three-compartment model, which we use to simulate the 24-h concentration history of VOCs in the shower, bathroom, and remaining household volumes resulting from the use of contaminated tap water. An important input to this model is the transfer efficiency of the VOC from water to air. The experiments reveal that the transfer efficiency of TCE from shower water to air has an arithmetic mean value of 61 percent and an arithmetic standard deviation of 9 percent. Analysis of the results shows that there is no statistically significant difference between the transfer efficiency measured with hot (37 degrees C) or cold (22 degrees C) shower water and that there is no statistically significant change in transfer efficiency with time during a 20-min shower. The implications for exposure assessment are considered.

The transfer of trichloroethylene (TCE) from a shower to indoor air: experimental measurements and their implications.

Experiments were performed to measure the transfer of trichloroethylene (TCE), a volatile organic compound (VOC), from tap water in showers to indoor air. In these experiments, the loss of TCE from tap water in the shower is based on the difference between influent and effluent concentrations. We have developed and previously published a three-compartment model, which we use to simulate the 24-h concentration history of VOCs in the shower, bathroom, and remaining household volumes resulting from the use of contaminated tap water. An important input to this model is the transfer efficiency of the VOC from water to air. The experiments reveal that the transfer efficiency of TCE from shower water to air has an arithmetic mean value of 61 percent and an arithmetic standard deviation of 9 percent. Analysis of the results shows that there is no statistically significant difference between the transfer efficiency measured with hot (37 degrees C) or cold (22 degrees C) shower water and that there is no statistically significant change in transfer efficiency with time during a 20-min shower. The implications for exposure assessment are considered.

The bioavailability of sediment-sorbed chlorobenzenes to larvae of the midge, Chironomus decorus.

Larval stages of the midge, Chironomus decorus, were used to define the bioaccumulation of sediment-sorbed mono-, di-, tri-, and hexachlorobenzene. Larvae were exposed to high- and low-organic-content sediments that had been equilibrated with individual radiolabeled chlorobenzenes prior to testing. Equilibrium or nonequilibrium aqueous concentrations of the volatile test chemicals were flowed through sealed chambers in a sediment-water exposure system. The uptake of chlorobenzenes by midge larvae was rapid for all compounds tested, and apparent steady-state conditions were reached within 48 hr of exposure. Bioconcentration factors for the accumulation of chlorobenzenes from sediments and from interstitial and overlying waters were related to the octanol/water partition coefficients of the compounds. Because the diffusion of chlorobenzenes to overlying water during nonequilibrium flow through conditions was very slow, bioaccumulation was dependent on the concentration of the chemicals in interstitial water. These results show how benthic organisms may be able to accumulate significant levels of chlorinated aromatic compounds from ecosystems where their concentrations in the water column are relatively low.

The influence of organic chelators on the toxicity of copper to embryos of the Pacific oyster, Crassostrea gigas.

The effects of copper on the development of Crassostrea gigas embryos were determined with a 48-hr static bioassay. In filtered, sterilized seawater from Bodega Bay, California, the LC100 was 20 microgram Cu/L, and the LC50 was 12 microgram Cu/L. Destruction of the naturally occurring dissolved organic material in the culture water by UV oxidation decreased embryo survival at 10 microgram Cu/L. The addition to seawater of five organic chelators (ethylenediaminetetraacetic acid (EDTA), sodium citrate, glycine, and oxalate at 1 x 10(-6) M, and humic matter at 2 mg/L) increased embryo survival. EDTA and humic matter were the most effective chelators; EDTA significantly increased survival at 100 microgram Cu/L and humic matter did so at 40 microgram Cu/L. The ability of a chelator to increase survival was related to the stability constant of the copper-chelator complex.