In order to determine whether characterization of organic carbon (OC) in particulate matter (PM) is limited due to the extraction or analysis, we have evaluated the OC extractability from three model PM matrices (wood smoke, diesel exhaust, and urban PM). We have compared hot pressurized water (HPW) fractionation and sequential organic solvent Soxhlet extraction. The evaluation of extraction efficiency was based on three methods: thermal optical transmittance (TOT), reflectance, and total organic carbon analyses. For all three PM samples, comparable OC yields were obtained with both extraction methods accounting for ∼45-60% of the total OC found in PM (based on TOT). These recoveries also suggest that a significant portion of OC in all PM materials remains unextractable. Further investigation of OC distribution in different polarity fractions using spectrometric techniques (including gas chro
Direct measurement of the n-octanol partition coefficients (K OW ) for highly hydrophobic organic chemicals is extremely difficult because of the extremely low concentrations present in the water phase. n-Butanol/water partition coefficients (K BW ) are generally much lower than K OW due to the increased solubility of solute in the alcohol saturated aqueous phase, and therefore become easier to measure. We measured the K BW for 25 neutral organic chemicals having measured log K OW s ranging from 2 to 9 and 4 additional highly hydrophobic chemicals, with unmeasured K OW s, having estimated log K OW s ranging from 6 to 18. The measured log K BW and log K OW values were linearly related, r 2 = 0.978, and using the regression developed from the data, K OW s were predicted for the 4 highly hydrophobic chemicals with unmeasured K OW s. The resulting predictions were orders of magnitude lower than those predicted by a variety of computational models and suggests the estimates of K OW in the literature for highly hydrophobic chemicals (i.e., log K OW greater than 10) are likely incorrect by several orders of magnitude.
The effects on juvenile rainbow trout survival, growth, food consumption, and food conversion efficiency from dietborne exposures to inorganic arsenic (arsenite, arsenate) and to the organoarsenicals monomethylarsonate (MMA), dimethylarsinate (DMA), and arsenobetaine (AsB) were investigated in two experiments: (1) a 28-d exposure using a live diet of oligochaete worms separately exposed via water to these five arsenic compounds and (2) a 56-d exposure using a pellet diet prepared from commercial fish food to which arsenite, MMA, or DMA were added. In the live diet experiment, the degree to which worms could be contaminated with the organoarsenicals was limited by toxicity to the worms and other experimental constraints, so that their toxicity relative to inorganic arsenic could not be fully established, but AsB was concluded to have low toxicity, consistent with published results for mammals. For the pellet diet experiment, MMA and DMA were found to be at least an order of magnitude less toxic than inorganic As on the basis of concentration in the diet, as well as much less toxic on the basis of accumulation in the fish. The need to consider speciation in aquatic risk assessments for arsenic was further demonstrated by tissue analyses of three macroinvertebrate species from a mining-impacted stream, which showed large variations in both total arsenic and the relative amounts of inorganic and organic arsenic. Additionally, although effects of arsenic on trout appear to be well correlated with inorganic arsenic, worms were found to be more sensitive to waterborne DMA than to inorganic arsenic, showing that low toxicity of organoarsenicals cannot be assumed for all aquatic organisms. Various difficulties in evaluating and applying studies on dietborne exposures and fish growth are also discussed.
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