Superfund sites that are contaminated with lead and undergoing remedial action generate lead -enriched dust that can be released into the air. Activities that can emit lead -enriched dust include demolition of lead smelter buildings, stacks, and baghouses; on -site traffic of heavy construction vehicles; and excavation of soil. Typically, air monitoring stations are placed around the perimeter of a site of an ongoing remediation to monitor air lead concentrations that might result from site emissions. The National Ambient Air Quality ( NAAQ ) standard, established in 1978 to be a quarterly average of 1.5 g / m 3 , is often used as a trigger level for corrective action to reduce emissions. This study explored modeling approaches for assessing potential risks to children from air lead emissions from the RSR Superfund site in West Dallas, TX, during demolition and removal of a smelter facility. The EPA Integrated Exposure Uptake Biokinetic ( IEUBK ) model and the International Commission of Radiologic Protection ( ICRP ) lead model were used to simulate blood lead concentrations in children, based on monitored air lead concentrations. Although air lead concentrations at monitoring stations located in the downwind community intermittently exceeded the NAAQ standard, both models indicated that exposures to children in the community areas did not pose a significant long -term or acute risk. Long -term risk was defined as greater than 5% probability of a child having a long -term blood lead concentration that exceeded 10 g / dl, which is the CDC and the EPA blood lead concern level. Short -term or acute risk was defined as greater than 5% probability of a child having a blood lead concentration on any given day that exceeded 20 g / dl, which is the CDC trigger level for medical evaluation ( this is not intended to imply that 20 g / dl is a threshold for health effects in children exposed acutely to airborne lead ). The estimated potential long -term and short -term exposures at the downwind West Dallas community did not result in more than 5% of children exceeding the target blood lead levels. The models were also used to estimate air lead levels for short -term and long -term exposures that would not exceed specified levels of risk ( risk -based concentrations, RBCs ). RBCs were derived for various daily exposure durations ( 3 or 8 h / day ) and frequencies ( 1 -7 days / week ). RBCs based on the ICRP model ranged from 0.3 ( 7 days / week, 8 h / day ) to 4.4 g / m 3 ( 1 day / week, 3 h / day ) for long -term exposures and were lower than those based on the IEUBK model. For short -term exposures, the RBCs ranged from 3.5 to 29.0 g / m 3 . Recontamination of remediated residential yards from deposition of air lead emitted during remedial activities at the RSR Superfund site was also examined. The predicted increase in soil concentration due to lead deposition at the monitoring station, which represented the community at large, was 3.0 mg / kg. This potential increase in soil lead concentration was insignificant, less th...
In 1996, the U.S. Environmental Protection Agency (USEPA) developed the Adult Lead Methodology (ALM) to provide an interim approach to assessing risks from non-residential exposures to lead. Because such exposures often involve occupational activities of adults, the ALM was directed at assessing soil-related lead risks to adults. Consistent with other approaches used in Superfund risk assessment, the ALM was designed to predict quasi-steady state blood lead concentrations (PbB) that might result from soil exposure. These predictions are converted to a risk estimate, expressed as the probability of exceeding a PbB level of concern. To examine the assumptions and variables in the ALM that have become available since 1996, a comparison was made of the attributes of seven alternative research models for which adequate documentation is available to understand and implement each approach. Several of these models have been used in regulatory decision-making; however, the USEPA has officially embraced none for general use. This analysis suggests that the ALM can continue to serve as a reasonable tool for assessing risks associated with non-residential exposures to soil. Under certain circumstances other models may be more applicable (i.e ., for assessing acute or intensive exposures); however, the ALM is recommended for the majority of risk assessment applications.
Crayfish were exposed to 50, 200, or 1000 μg/mL ethylene glycol (EG) daily for 61 days, and were subsequently transferred to clean water for a 67‐day decontamination phase. During uptake and loss, samples were analyzed for EG in gills, muscle, gastrointestinal tract, and hepatopancreas. An open one‐compartment mathematical model described the uptake and loss phases data. Uptake was dependent upon the aqueous concentration of EG. Crayfish did not concentrate EG above the water concentration. Bioaccumulation factors for the selected tissues at 61 days of exposure to 50, 200, and 1000 μg/mL EG, respectively were as follows: 0.40, 0.21, and 0.21 for gills; 0.48, 0.21, and 0.21 for muscle; 0.61, 0.42, and 0.27 for gastrointestinal tract; and 0.60, 0.33, and 0.22 for hepatopancreas. Time to equilibrium was 5,4,5, and 4 days for gills, muscle, gastrointestinal tract, and hepatopancreas, respectively, at 50 μg/mL aqueous concentration; 5, 4, 6, and 4 days, respectively, at 200 μg/mL aqueous concentration; and 7, 5, 7, and 5 days, respectively, at 1000 μg/mL aqueous concentration. Crayfish eliminated the accumulated EG within 5 days for animals exposed to 50 μg/mL EG and 6 days for those exposed to 200 and 1000 μg/mL EG. © 1993 John Wiley & Sons, Inc.
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