Concentrate processing environmental exposures

As part of TSCA, EPA can require the testing of any chemical if there is the possibiUty of an unreasonable risk to health or environment or if there is significant human or environmental exposure. If the substance poses an unreasonable risk, EPA can prohibit the manufacture, processing, or distribution of the substance limit the amount of the substance that can be manufactured, processed, or distributed prohibit a particular use for the substance limit the concentration of the substance during manufacture, processing, or distribution regulate disposal methods for the substance and require manufacturers to maintain records of process and to conduct tests to assure compliance with EPA rules. 

Tier 2 PRA process involved developing environmental exposure data and chronic toxicity data distributions for individual POPs. The mean concentrations of POPs in local marine water measured at various locations were used as exposure data in the construction of the exposure distribution. The chronic toxicity data distribution was established based on published international acute toxicity data (LC50, EC50) on a variety of aquatic organisms tested in many jurisdictions, drawn primarily from the USEPA ECOTOX database (2002) (available at http //www.epa.gov/ ecotox). If the upper 5th centile of the measured chemical exposure data distribution did not exceed the lower 5th centile of its estimated chronic toxicity distribution, the potential ecological risk posed by the chemical was judged to be tolerable (Hall and Giddings, 2000). 

Natural attenuation (NA) refers to the reduction of contaminant concentrations in environmental media by processes such as dilution, dispersion, sorption, volatilization, and biotic or abiotic transformations. As a passive remediation approach, NA is mostly applied in connection with organic contaminants which migrate from the source in groundwater. Naturally attenuating contaminant plumes show a decline in the dissolved contaminant mass as a function of time, and a decline in contaminant concentrations downgradient from the source. Before potential receptor exposure points are reached, natural attenuation is expected to reduce dissolved contaminant concentrations below regulatory standards (Wiedeme-ier et al. 1999). 

In determining the relative risk posed by pollutants in soils, it is not enough to simply measure the chemical concentration. It is also necessary to address the risk-assessment paradigm, the pathways by which human health and the environment can be affected, and the availability of the released chemical for transport and adverse impact (Loehr, 1996). Environmental risk is commonly defined as the adverse impact resulting from human or environmental exposure (real or potential) to contaminants under site-specific circumstances. But while decisions on the suitability of soil-remediation processes commonly focus on chemical-concentration... 

The assessment of risk normally requires an evaluation of the intrinsic physico-chemical properties, i.e. biodegradability and toxicity, of the chemical. The risk assessment for surfactants is usually based on biodegradability and aquatic toxicity data. Generally in environmental exposure assessment, the concentration of a substance in the different environmental compartments is estimated from the amount of the substance released from domestic and industrial use. The PEC can therefore be calculated from a knowledge of the quantity of the substance that will be discharged (e.g. via waste-waters) into the environment and the distribution and degradation processes (e.g. waste-water treatment plant). 

The physicochemical hazard assessment must consider the potential threats from combustion, explosiveness, oxidizability, and metal corrosion. The human health risk assessment must qualitatively rank the hazard presented by the new substance, and the submitter must provide "the doses (concentration) of the new chemical substance. .. to match its no-hazard or minimum hazard status," akin to a DNEL as described in Chapter 2. The environmental hazard assessment must qualify the hazard level as severe, medium, or mild and a concentration akin to the PNEC, as discussed in Chapter 2, derived. The exposure assessment comprises two parts a simple exposure forecast and assessment and a detailed exposure forecast and assessment. The latter includes a material balance on manufacturing or processing, and exposure scenarios for different exposure routes that describe the extent, range, and frequency of exposures. The results of the hazard... 

There are other strategies to deal with the factors that accelerate fatigue listed in Section 1.5. Perhaps most important, apart from the material of manufacture, is paying particular attention to the manufacturing process. The aim is to minimize internal and surface defects that concentrate stresses. One can also engineer temperature control and environmental exposure. 

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