PubMed · 14434489
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P POTTS, J I BOWRING. 1960. Exercise in a weightless environment.. https://pubmed.ncbi.nlm.nih.gov/14434489/
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Legal and regulatory authorities around the world generally require that risk assessments are undertaken for the licensing of new and existing substances that present high risk to the environment or the human health. This applies to 'down-the-drain' chemicals that are usually found in household products, such as detergents, that are mainly discharged into rivers via sewer systems. However, the data available for these chemicals is often limited due to cost constraints: in particular, concentration time series for works effluent are generally unavailable, even load data for specific works is often scarce. Although a wide range of models are available, there is a general lack of knowledge on their suitability to model the fate of down-the-drain chemicals at the catchment scale. Several models are presented in this review. The models selected are: the Mackay models, EUSES, Mike 11, QUAL2E, TOMCAT and GREAT-ER. Various applications of these models were investigated to investigate their strength and weaknesses. It appears that, where the availability of data is limited, multimedia fate models such as the Mackay models and EUSES may best be applied to estimate the global risk within each media. However, for site-specific risk assessment the GREAT-ER in-stream water quality model was considered to be more appropriate for modelling down-the-drain chemicals, because it accounts for both spatial and temporal variability, while its data requirements are lower than for models such as Mike 11 and QUAL2E.
We conducted a statistical analysis to discern the relative strengths of the loading of various forms of nitrogen, phosphorus, dissolved silicate and their molar ratios on the variance in the size of the summertime low oxygen zone found off the Mississippi River, northern Gulf of Mexico. A stable statistical model that included Year and riverine nitrate+nitrite loading for the 2 months prior to the measurement of hypoxic zone size described 82% of its variation in size from 1978 to 2004. The usefulness of the term Year is consistent with the documented increase in carbon stored in sediments after the 1970s, which is when the hypoxic zone is predicted to have become a regular feature on the shelf and to have expanded westward. The increased carbon storage is anticipated to cause a sedimentary respiratory demand influencing the size of the zone, and whose temporal influence is cumulative and transcends the annual variations in nitrogen loading. The variable Year is negatively correlated with the TN:TP ratio in a way that suggests N, not P, has become more important as a factor limiting phytoplankton growth in the last 20 years. Nitrogen, in particular nitrate+nitrite, and not phosphorus, dissolved silicate, or their molar ratios, appears to be the major driving factor influencing the size of the hypoxic zone on this shelf. This conclusion is consistent with cross-system analyses that conclude that the TN:TP ratio in the Mississippi River, currently fluctuating around 20:1, is indicative of nitrogen, not phosphorus, limitation of phytoplankton growth. Nutrient management that places stronger emphasis on reducing nitrogen loading as compared to phosphorus loading, is justified.
A novel approach to determine size-segregated particle number emission factors for traffic is presented. It was proven that using limited data sets (800-2000 samples) statistically significant emission factors from road traffic can be extracted. In this study data from four sites were used for calculating emission factors (rural and urban roadside, urban rooftop, and urban background). The measurements were performed using SMPS/DMPS (scanning or differential particle sizers) from TSI and commercial gas analyzers. Describing the particle concentration as a ratio to an exhaust trace gas, e.g. NOx, the dilution effect will be minimized. This ratio is easily compared among different studies. By knowledge of the emission factor of the chosen trace gas the emission ratio can be converted to an emission factor for particle numbers of defined particle sizes. For the presented method only one measurement site is needed, where the difference between high and low (background) traffic exposure is used. To define high and low traffic exposure, the best result was obtained using high ratio of [NO] to [NO2] and low [NOx], respectively. Emission ratios for 10-100-nm particles at two road sites, one high-speed 90-kmph rural case and one urban, slower, and more congested situation, were determined to (35 +/- 15) x 10(14) and (24 +/- 8) x 10(14) particles per mole NOx, respectively.