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Pollman C.D.,Aqua Lux Lucis Inc. | Axelrad D.M.,Florida A&M University
Science of the Total Environment | Year: 2014

While bioaccumulation factors (BAF) - the ratio of biota contaminant concentrations (Cbiota) to aqueous phase contaminant concentrations (Cw) - are useful in evaluating the accumulation of mercury (Hg) and other contaminants for various trophic levels in aquatic ecosystems, reduction of the underlying relationship between Cbiota and Cw to a single ratio (BAF) has inherent risks, including spurious correlation. Despite a long and rich history of remonstrations in the literature, several very recent publications evaluating Hg-related BAFs have suffered from false conclusions based on spurious correlation, and thus it seems that periodic reminders of the causes and risks of these errors are required. Herein we cite examples and explanations for unsupported conclusions from publications where authors using BAF-Cw relationships fail to recognize the underlying statistical significance (or lack thereof) of direct relationships between Cw and Cbiota. This fundamental error leads to other problems, including ascribing mechanistic significance (e.g., mechanisms related to biota contaminant uptake) to "inverse" BAF-Cw relationships that reflect nothing more than regressing the log transformed inverse of Cw (i.e., negative log) against itself (i.e., positive log transformed), and using such regression models of BAF-Cw relationships that appear significant for predictive purposes, but are misleading. Spurious correlation arising in the analysis of BAF relationships can potentially appear in more subtle forms as well, including regressing variables such as dissolved organic carbon (DOC) that are correlated with Cw. We conclude that conducting a direct analysis by examining the relationship between Cbiota and Cw (or Cbiota and other variables) rather than evaluating a ratio (BAF) is less ambiguous and subject to error, more easily interpreted, and would lead to more supportable conclusions. © 2014 Elsevier B.V.. Source


Pollman C.D.,Aqua Lux Lucis Inc. | Axelrad D.M.,Florida A&M University
Bulletin of Environmental Contamination and Toxicology | Year: 2014

The Everglades, an ecosystem of international significance, has elevated biota mercury levels representing risk to human and wildlife consumers of fish. Given the critical role of sulfate in the methylation of mercury, and because there is a significant agricultural contribution, one potential means of reducing these mercury levels is reducing Everglades sulfate inputs. Julian II (Bull Environ Contam Toxicol 90:329-332, 2013) conducted regression modeling of the relationship between surface water sulfate concentrations and Gambusia spp. mercury bioconcentration factors across the major hydrologic subunits of the Everglades, and used those results to draw conclusions about the role of sulfate in the cycling of mercury in the Everglades. We however demonstrate a number of fundamental problems with the analysis, interpretation and conclusions. As a result, we strongly caution against using the results of Julian II (Bull Environ Contam Toxicol 90:329-332, 2013) to formulate management decisions regarding mitigation of the Everglades mercury problem. © 2014 Springer Science+Business Media New York. Source


Harris R.,Reed Harris Environmental Ltd | Pollman C.,Aqua Lux Lucis Inc. | Landing W.,Florida State University | Evans D.,National Oceanic and Atmospheric Administration | And 11 more authors.
Environmental Research | Year: 2012

Gulf of Mexico (Gulf) fisheries account for 41% of the U.S. marine recreational fish catch and 16% of the nation's marine commercial fish landings. Mercury (Hg) concentrations are elevated in some fish species in the Gulf, including king mackerel, sharks, and tilefish. All five Gulf states have fish consumption advisories based on Hg. Per-capita fish consumption in the Gulf region is elevated compared to the U.S. national average, and recreational fishers in the region have a potential for greater MeHg exposure due to higher levels of fish consumption. Atmospheric wet Hg deposition is estimated to be higher in the Gulf region compared to most other areas in the U.S., but the largest source of Hg to the Gulf as a whole is the Atlantic Ocean (>90%) via large flows associated with the Loop Current. Redistribution of atmospheric, Atlantic and terrestrial Hg inputs to the Gulf occurs via large scale water circulation patterns, and further work is needed to refine estimates of the relative importance of these Hg sources in terms of contributing to fish Hg levels in different regions of the Gulf. Measurements are needed to better quantify external loads, in-situ concentrations, and fluxes of total Hg and methylmercury in the water column, sediments, and food web. © 2012 Elsevier Inc. Source


Harris R.,Reed Harris Environmental Ltd | Pollman C.,Aqua Lux Lucis Inc. | Hutchinson D.,Reed Harris Environmental Ltd | Landing W.,Florida State University | And 4 more authors.
Environmental Research | Year: 2012

A mass balance model of mercury (Hg) cycling and bioaccumulation was applied to the Gulf of Mexico (Gulf), coupled with outputs from hydrodynamic and atmospheric Hg deposition models. The dominant overall source of Hg to the Gulf is the Atlantic Ocean. Gulf waters do not mix fully however, resulting in predicted spatial differences in the relative importance of external Hg sources to Hg levels in water, sediments and biota. Direct atmospheric Hg deposition, riverine inputs, and Atlantic inputs were each predicted to be the most important source of Hg to at least one of the modeled regions in the Gulf. While incomplete, mixing of Gulf waters is predicted to be sufficient that fish Hg levels in any given location are affected by Hg entering other regions of the Gulf. This suggests that a Gulf-wide approach is warranted to reduce Hg loading and elevated Hg concentrations currently observed in some fish species. Basic data to characterize Hg concentrations and cycling in the Gulf are lacking but needed to adequately understand the relationship between Hg sources and fish Hg concentrations. © 2012. Source


James R.T.,South Florida Water Management District | Pollman C.D.,Aqua Lux Lucis Inc.
Lake and Reservoir Management | Year: 2011

Two separate models, the Internal Loading Phosphorus Model (ILPM) and the Lake Okeechobee Water Quality Model (LOWQM) were used to predict outcomes of 3 alternatives to reduce internal sediment loads: (1) the baseline simulation, which reduced external phosphorus (P) loads over time to meet the total maximum daily load of 140 metric tons to the lake by 2015; (2) the baseline plus a large-scale chemical treatment, which used alum to bind sediment P; and (3) the baseline plus a large dredging project, which removed P-laden sediments. The ILPM and LOWQM differed greatly in their approach to simulate water quality, but their predictions for each scenario were similar. The baseline showed progressive improvements of water quality that approached the in-lake restoration goal of 40 g P/L within 40 years; chemical treatment predicted this goal would be reached in 15 years; and dredging would potentially meet the goal within 30 years. Increasing or reducing the effectiveness of each treatment resulted in higher or lower predicted total phosphorus concentrations, respectively, but little change in the overall time line. An economic analysis found that in 2002 USD, chemical treatment would cost $500 million and dredging would cost $3 billion. Based on the model results, the economic analysis and other comprehensive technical evaluations of the scenarios, the baseline simulation was recommended as the preferred plan, and the management focus will remain on reduction of external P loads. © 2011 by the North American Lake Management Society. Source

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