Arsenic and thallium data in environmental samples: Fact or fiction?

Matrix effects may increasingly lead to erroneous environmental decisions as regulatory limits or risk‐based concentrations of concern for trace metals move lower toward the limits of analytical detection. A U.S. Environmental Protection Agency Office of Technical Standards Alert estimated that environmental data reported using inductively coupled plasma spectrometry (ICP‐AES) has a false‐positive rate for thallium of 99.9 percent and for arsenic of 25 to 50 percent. Although this does not seem to be widely known in the environmental community, using three case studies, this article presents data in environmental samples that demonstrate severe matrix effects on the accuracy of arsenic and thallium results. Case Study 1 involves soil results with concentrations that approached or exceeded the applicable regulatory soil cleanup objectives of 13 mg/kg for arsenic and 2 mg/kg for thallium. Reanalysis using ICP coupled with a mass spectrometer (ICP‐MS) confirmed all thallium results were false positives and all arsenic results were biased high, concluding no action was required for soil remediation. Case Study 2 involves groundwater results for thallium at a Superfund site, where thallium was detected in groundwater up to 21.6 μ g/L using ICP‐AES. Reanalysis by ICP‐MS reported thallium as nondetect below the applicable regulatory level in all samples. ICP‐MS is usually a more definitive and accurate method of analysis compared to ICP‐AES; however, this is not always the case, as we demonstrate in Case Study 3, using data from groundwater samples at an industrial site. Through a weight‐of‐evidence approach, it is demonstrated that although method quality control results were acceptable, interferences in some groundwater samples caused biased high results for arsenic using ICP‐MS, which were significantly lower when reanalyzed using hydride generation atomic fluorescence spectrometry. Causes of these interference effects and conclusions from the three case studies to obtain accurate metal data for site assessment, risk characterization, and remedy selection are discussed. © 2010 Wiley Periodicals, Inc.     

In situ experiment to determine advective-diffusive controls on solute transport in a clay-rich aquitard

Solute transport in clay-rich aquitards is characterized as molecular diffusion- or advection-dominated based on the Péclet number (P(e)). However, few field-based measurements of the coefficient of molecular diffusion (D(e)) exist, and none with a range of advection- or diffusion-dominated conditions in the same aquitard. In this long-term field experiment, standing water in a recovering well was spiked with deuterium ((2)H), then water-level recovery and δ(2)H values were monitored as the well returned to static conditions over 1054 days. After a second (2)H spike, water levels and δ(2)H values were monitored to day 1644 while under near static conditions. Modeling of the second spike was used to define the D(e) of (2)H as (3-4)× 10(-10)m(2)s(-1) for an accessible porosity of 0.31. Reservoir concentrations from the initial spike were modeled to define the transition from advection- to diffusion-dominated transport. This occurred after 200 days, consistent with a transition in P(e) from <1 to >1 when the length term is taken as the radial extent of the tracer plume (normalized concentration <0.05). This study verifies plume extent as the characteristic length term in the calculation of P(e) and demonstrates the transition from advection- to diffusion-dominated transport as the value of P(e) decreases below unity.     

The Use of Health Risk Assessment to Estimate Desirable Sampling Detection Limits

Abstract

The inclusion of non-detected chemicals in a health risk assessment may lead, in some cases, to estimated risks that exceed regulatory thresholds, because one must use the detection limit or half of the detection limit. This study presents a methodology which will allow one to estimate appropriate detection limits by conducting a health risk assessment prior to the source sampling program. The advantages and shortcomings of various levels of detail in the risk assessment to determine those detection limits are discussed. The application of the methodology is demonstrated with a case study of the potential health effects of power plant stack emissions.     

Elemental Carbon Concentration in the Air Around Tampa Bay,Florida, 1990-1991

Elemental carbon (EC) particles have been found in the lungs of dolphins. The question arose as to whether these particles originated over land or water. This project determined the amount of EC particulate found in terrestrial air. Portions of paniculate filters and associated data collected during the period from January 1990 through December 1991 were provided by the Florida Department of Environmental Regulation. Using reflectance spectroscopy and laboratory-generated standards, atmospheric concentrations of EC and TSP were determined. This paper addresses the data from those counties which surround Tampa Bay.

In the spring of 1992, a television news station reported that researchers at Mote Marine Institute had found black carbon particulates in the lungs of dolphins (reported as “...dolphins with Black Lung Disease..."). The dolphins were found in the Gulf of Mexico off the coast of Florida.1 In discussions with a principal investigator of the dolphin study, the question arose as to whether these particulates came from urban or marine sources. No comprehensive investigation of soot concentrations in the air over Florida had been made. This study reports the elemental carbon (EC) content of urban particulate matter in the Tampa Bay region, where the affected dolphins were discovered between 1988 and 1990 (Sarasota County). This is the first step toward answering whether urban concentrations of EC were sufficient to contribute measurably to the EC found in the marine environment. Future efforts will address marine concentrations and sources of EC.

Elemental carbon, commonly termed “soot,” is a product of incomplete combustion. Common urban sources of EC in particulate matter include both mobile sources (diesel-powered buses, cars, and trucks) and point sources (incinerators, power plants and home heating units). The State of Florida operates environmental monitoring stations in selected municipalities around the state. At these stations, which were sited according to EPA requirements², Total Suspended Particulate (TSP) samples were collected using the accepted methods.³ These samples were suitable for EC analysis. Samples collected in the Tampa Bay region in 199b and 1991 were analyzed for EC content using reflectance spectroscopy. EC concentrations were calculated in micrograms per cubic meter (μg/m³).     

Asbestos: Rationale Behind A Proposed Air Quality Standard

A computerized simulation model has been developed to compute energy requirements of a limestone slurry flue gas desulfurization (FGD) system as a function of FGD system design parameters, power plant characteristics, coal properties, and sulfur dioxide emission regulation. Results are illustrated for a "base case" plant of 500 MW, burning 3.5% sulfur coal, meeting the federal new source performance standard of 1.2 lb SO₂/10⁶ Btu. The flue gas is cleaned by an electrostatic precipitator followed by a limestone FGD system with a TCA scrubbing vessel and an optimized in-line steam reheater. The total FGD system energy requirement for this case was found to be 3.4% of the total energy input to the boiler. Sensitivity analyses were then performed in which the nominal values of ten system parameters were individually varied. This caused the total FGD system energy requirement to vary between 2.5 % and 6.1 % of the gross plant output for the range of parameters tested. The most sensitive parameters were found to be scrubbing slurry pH, which affects pumping requirements, and stack gas exit temperature, which affects reheat requirements. In all cases, FGD energy requirements were minimized when the SO₂ emission standard was met by partially bypassing the scrubber. In light of the recent Clean Air Act Amendments this option may not be feasible in the future.     

Effects of the Motor Vehicle Control Program On Hydrocarbon Concentrations in The Central Los Angeles Atmosphere

The body of information presented in this paper is directed to those individuals concerned with the effect of the motor vehicle control program on ambient hydrocarbon concentrations in a metropolitan area during peak traffic hours. The data used in this study are from gas chromatographic analyses of air samples taken in 1963-65, before implementation of the exhaust control program for new motor vehicles, and in 1971 and 1973, after several years’ application of this program. A brief history of the motor vehicle program in California together with emission standards for hydrocarbons are discussed and certain automobile-related hydrocarbons are identified and characterized. Frequency distributions were constructed for total hydrocarbons, non-methane hydrocarbons, methane, acetylene, and isopentane for 1963-65, 1971, and 1973 and the standard deviation (1 sigma) concentration limits are discussed for each of the subgroups mentioned above. The average concentration and relative percent comparisons for methane, ethane, n-butane, isopentane, C₃+ paraffin, eth-ene, propene, C₄ +olefin, acetylene, benzene, and toluene are shown and discussed in detail. These studies: 1) show hydrocarbon emissions from motor vehicles were reduced 47.6% during this time period; 2) indicate selective reduction of compounds; and 3) reveal a 51.8% reduction in the 1973 ambient total hydrocarbon concentration since 1963-65.     

Aerobic Biodegradation of Hydrocarbons in High Temperature and Saline Groundwater

A series of laboratory microcosm experiments and a field pilot test were performed to evaluate the potential for aerobic biodegradation of aromatic hydrocarbons and methyl tert‐butyl ether (MtBE; a common oxygenate additive in gasoline) in saline, high temperature (>30° C) groundwater. Aquifer, sediment, and groundwater samples from two sites, one in Canada and another in Saudi Arabia, were incubated for 106 days to evaluate the changes in select hydrocarbon and MtBE concentrations and microbial community structure. Almost complete biodegradation of the aromatic hydrocarbons was found in the Saudi Arabian microcosm samples whereas the Canadian microcosm samples showed no significant biodegradation during the laboratory testing. MtBE degradation was not observed in either set of microcosms. Denaturing gradient gel electrophoresis analyses showed that, while the Canadian microorganisms were the most diverse, they showed little response during incubation. The microbial communities for the Saudi Arabian sample contained significant numbers of microorganisms capable of hydrocarbon degradation which increased during incubation. Based on the laboratory results, pilot‐scale testing at the Saudi Arabian field site was carried out to evaluate the effectiveness of enhanced aerobic biodegradation on a high temperature, saline petroleum hydrocarbon plume. Dissolved oxygen was delivered to the subsurface using a series of oxygen diffusion emitters installed perpendicular to groundwater flow, which created a reactive zone. Results obtained from the seven‐month field trial indicated that all the target compounds decreased with removal percentages varying between 33 percent for the trimethylbenzenes to greater than 80 percent for the BTEX compounds. MtBE decreased 40 percent on average whereas naphthalene was reduced 85 percent on average. Examination of the microbial population upgradient and downgradient of the emitter reactive zone suggested that the bacteria population went from an anaerobic, sulfate‐reducing dominated population to one dominated by a heterotrophic aerobic bacteria dominant population. These studies illustrate that field aerobic biodegradation may exceed expectations derived from simple laboratory microcosm experiments. Also, high salinity and elevated groundwater temperature do not appear to inhibit in situ aerobic biorestoration. © 2014 Wiley Periodicals, Inc.     

Differences in sensitivity to the fungal pathogen Batrachochytrium dendrobatidis among amphibian populations

Contributing to the worldwide biodiversity crisis are emerging infectious diseases, which can lead to extirpations and extinctions of hosts. For example, the infectious fungal pathogen Batrachochytrium dendrobatidis (Bd) is associated with worldwide amphibian population declines and extinctions. Sensitivity to Bd varies with species, season, and life stage. However, there is little information on whether sensitivity to Bd differs among populations, which is essential for understanding Bd‐infection dynamics and for formulating conservation strategies. We experimentally investigated intraspecific differences in host sensitivity to Bd across 10 populations of wood frogs (Lithobates sylvaticus) raised from eggs to metamorphosis. We exposed the post‐metamorphic wood frogs to Bd and monitored survival for 30 days under controlled laboratory conditions. Populations differed in overall survival and mortality rate. Infection load also differed among populations but was not correlated with population differences in risk of mortality. Such population‐level variation in sensitivity to Bd may result in reservoir populations that may be a source for the transmission of Bd to other sensitive populations or species. Alternatively, remnant populations that are less sensitive to Bd could serve as sources for recolonization after epidemic events.