Papers by Robert N. Brent
Environmental Toxicology and Chemistry, 2021
The potential for delayed mortality following short-term episodic pollution events was evaluated ... more The potential for delayed mortality following short-term episodic pollution events was evaluated by exposing cladocerans (Ceriodaphnia dubia) and rainbow trout (Oncorhynchus mykiss) to zinc (Zn) in various 1-to 48-h and 1-to 96-h exposures, respectively, followed by transferring the exposed organisms to clean water for up to 47 h for C. dubia and up to 95 h for trout for additional observation. For C. dubia, 1-h exposures of up to 3790 µg Zn/L never resulted in mortality during the actual Zn exposures, but by 48 h, a 1-h exposure to 114 µg/L, a concentration similar to the present US national water quality acute criterion for the test water conditions, ultimately killed 70% of C. dubia. With C. dubia, the speed of action of Zn toxicity was faster for intermediate concentrations than for the highest concentrations tested. For rainbow trout, pronounced delayed mortalities by 96 h only occurred following ≥8-h exposures. For both species, ultimate mortalities from Zn exposures ≤8 h mostly presented as delayed mortalities, whereas for exposures ≥24 h, almost all ultimate mortalities presented during the actual exposure periods. With Zn, risks of delayed mortality following exposures to all concentrations tested were much greater for the more sensitive, small-bodied invertebrate (C. dubia) than for the less sensitive, larger-bodied fish (rainbow trout). These results, along with previous studies, show that delayed mortality is an important consideration in evaluating risks to aquatic organisms from brief, episodic exposures to some substances.
Journal of Environmental Chemical Engineering, 2017
Handheld X-ray fluorescence (XRF) devices hold promise for quick field screening of contaminated ... more Handheld X-ray fluorescence (XRF) devices hold promise for quick field screening of contaminated sites, but so far, these devices have not been successfully used for mercury screening because of poor sensitivity and questionable accuracy. This paper describes a site-specific calibration method and demonstrates the successful field use of XRF for measuring mercury in the soils of contaminated sites. The method achieved a detection limit of 7.4 mg/kg Hg with a 60-s analysis time. This improves upon earlier attempts and is sufficient for detecting mercury at generic risk assessment soil screening levels (23 mg/kg Hg). The study also demonstrated levels of accuracy and precision for the method that rivaled traditional laboratory methods. In a split-sample comparison with laboratory Method 7471A, field XRF results agreed with an R 2 of 0.93 and a median coefficient of variation of 15%. Precision estimates from duplicate and triplicate samples were not statistically different between the two methods and were constrained by sample heterogeneity and not method capabilities. This study demonstrates that handheld XRF can be successfully used at contaminated sites to achieve high quality Hg results that are accurate, precise, and at a level of sensitivity that is commensurate with generic risk assessment screening levels.
2006 Portland, Oregon, July 9-12, 2006, 2006
Environmental Toxicology and Chemistry, 1998
Conventional toxicity testing has relied heavily on fixed duration continuous exposure conditions... more Conventional toxicity testing has relied heavily on fixed duration continuous exposure conditions. These conditions have little relevance to the exposure conditions of many environmental pollutants, particularly the highly variable and often brief exposure regimes of episodic pollution events. This research was designed to assess the effects of brief exposures using a postexposure observation period. The common freshwater organisms Ceriodaphnia dubia,
TMDL 2010: Watershed Management to Improve Water Quality Proceedings, 14-17 November 2010 Hyatt Regency Baltimore on the Inner Harbor, Baltimore, Maryland USA, 2010
Proceedings of the Water Environment Federation, 2005
Archives of Environmental Contamination and Toxicology, 2011
Mercury is a globally distributed pollutant that biomagnifies in aquatic food webs. In the United... more Mercury is a globally distributed pollutant that biomagnifies in aquatic food webs. In the United States, 3781 water bodies fail to meet criteria for safe fish consumption due to mercury bioaccumulation. In the risk assessment and management of these impairments (through the total maximum daily load program), an important step is evaluating the relationship between aqueous mercury and mercury in fish tissue. Often, this relationship is simplified to a bioaccumulation factor (BAF): the ratio of fish tissue mercury to aqueous mercury. This article evaluates the relationship between aqueous mercury and fish tissue mercury across a contamination gradient in the South and South Fork Shenandoah rivers of Virginia. The relationship was found to be nonlinear, with BAFs decreasing as the level of contamination increased. This means that protective water column mercury concentration targets established from sitespecific BAFs will be overestimated in contaminated areas and will not be sufficiently protective. To avoid this overprediction in the South and South Fork Shenandoah rivers, an empirical nonlinear Michaelis-Menten model was used to establish a protective water-quality target. Among other models and variables, the Michaelis-Menten model, relating total mercury in the water column to methylmercury in fish tissue, achieved the best empirical fit (r 2 = 0.9562). The resulting water-quality targets using this model were 3.8 and 3.2 ng/l for the South and South Fork Shenandoah rivers, respectively. These values are 2.1-2.5 times lower than the water-quality target developed using a site-specific BAF. These findings demonstrate the need to consider nonlinear BAF relationships in mercury-contaminated areas.
Archives of Environmental Contamination and Toxicology, 2014
A B S T R A C T Handheld X-ray fluorescence (XRF) devices hold promise for quick field screening ... more A B S T R A C T Handheld X-ray fluorescence (XRF) devices hold promise for quick field screening of contaminated sites, but so far, these devices have not been successfully used for mercury screening because of poor sensitivity and questionable accuracy. This paper describes a site-specific calibration method and demonstrates the successful field use of XRF for measuring mercury in the soils of contaminated sites. The method achieved a detection limit of 7.4 mg/kg Hg with a 60-s analysis time. This improves upon earlier attempts and is sufficient for detecting mercury at generic risk assessment soil screening levels (23 mg/kg Hg). The study also demonstrated levels of accuracy and precision for the method that rivaled traditional laboratory methods. In a split-sample comparison with laboratory Method 7471A, field XRF results agreed with an R 2 of 0.93 and a median coefficient of variation of 15%. Precision estimates from duplicate and triplicate samples were not statistically different between the two methods and were constrained by sample heterogeneity and not method capabilities. This study demonstrates that handheld XRF can be successfully used at contaminated sites to achieve high quality Hg results that are accurate, precise, and at a level of sensitivity that is commensurate with generic risk assessment screening levels.
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Papers by Robert N. Brent