Showing papers in "Critical Reviews in Environmental Science and Technology in 1995"

A review: Pyrite oxidation mechanisms and acid mine drainage prevention

Abstract: Sulfide oxidation, part of sulfur's biotic/abiotic cycle, is an important natural phenomenon. However, because of the sulfide's association with metallic ores and fossil fuels in the form of pyrite (FeS2) and the world's increasing demand for metals and fossil fuels, sulfide oxidation in nature is in some state of perturbation. This perturbation, which results from land disturbances (e.g., mining, and/or ore processing), produces acid drainage often enriched with heavy metals. This acid drainage, commonly referred to as acid mine drainage (AMD), has become an economic and environmental burden. This review deals with abiotic/biotic modes of pyrite oxidation and the mechanistic involvement of OH‐, O2, and Fe3+ in the pyrite oxidation process in low/high pH environments. Also included is recent evidence on the potential involvement of CO2 in catalyzing pyrite oxidation in near‐neutral and alkaline environments. Finally, the review deals with various pyrite‐oxidation control approaches, the merits of...

Induction of cytochrome P450 as a biomarker for environmental contamination in aquatic ecosystems

Abstract: Representing toxicant‐induced changes in biological systems, biomarkers can serve as linkers between contamination (cause) and biological effects, and therefore provide unique information on ecosystem health. Hence, they are increasingly used for assessing the exposure of organisms to environmental contamination. Here, application of the induction of cytochrome P4501A (CYP1A), certainly the best studied biomarker, in field trials with freshwater and marine fish is reviewed. Moreover, the use of a number of other biomarkers, alone or in concert with CYP1A, is evaluated. Determination of CYP1A in field studies with fish has to consider several influencing factors, such as species, age, reproductive stage, temperature, and possible inhibitors. The overview shows that CYP1A induction is significantly related to contaminant levels in the environment in 93% of the investigated field studies. It is apparent that only certain classes of xenobiotica act as inducers of CYP1A (e.g., PAHs, coplanar PCBs, pol...

Urban stormwater quality: Summary of contaminant data

Abstract: Storm water quality can have a significant impact on receiving water bodies. Two of the major impacts can be to aquatic Ufe in the receiving water body and downstream water users that might use the water as a raw water source for drinking water. With increased understanding of the importance of drinking water quality to public health and the recognition that protecting raw water sources is an integral component of the water treatment process, there is a greater need to identify possible contaminants found in storm water that impact the receiving water quality. Presented is a literature review to identify and quantify contaminant data available on storm water. The article focuses on work that presented specific chemical, physical, and biological parameters rather than the traditionally used overall water quality parameters, such as biochemical oxygen demand and total suspended solids. To assess impacts and to put into perspective the importance of the reported concentrations, values were compared ...

Formation, distribution, and ecotoxicity of methylmetals of tin, mercury, and arsenic in the environment

Abstract: Findings on methylation of tin, mercury, and arsenic in the environment are reviewed. The development of separation and detection systems in trace analysis has made it possible to determine the concentration of these methylated forms in the environment. Abiological methylation mechanisms are similar for these three metals, and methylcobalamin and methyl iodide are thought to be the major methyl donors in the environment. Photochemical reaction and transalkylation produce methylmetals. Humic and fulvic acids are the factors affecting methylation. The research on biological methylation started from incubation with polluted water and sediments, and some exceptional reports cast doubt as to whether it was really biomethylation. Some organisms that can form methyl metals from their metal forms have been separated, and the mechanism has been investigated using the pure culture. Methylation of tin and mercury increases the toxicity of their original metal forms, while methylation of arsenic lowers its t...

Kinetic constraints on the loss of organic chemicals from contaminated soils: Implications for soil‐quality limits

Abstract: Generic or site-specific soil-quality limits for organic contaminants have been adopted or proposed in various countries in an effort to control or assess contamination. The most comprehensive generic limits, established in the Netherlands, distinguish between background concentrations for naturally occurring substances and analytical detection limits for man-made organic compounds (target values) and threshold concentrations above which remediation may be necessary (intervention values). These are being employed to highlight contaminated sites that require treatment/remediation, ideally resulting in the reduction of the compounds of concern. These limits have been derived in a number of ways but are largely based on professional judgment, usually on information concerning pathways of human exposure, phytotoxicity, and ecotoxicological effects. Effective remediation of contaminated soils is frequently limited by the slow kinetics of contaminant loss from soils under prevailing environmental conditions. This is frequently underestimated, even though it may be of fundamental importance in determining the success of treatment/remediation with respect to the assigned quality limits. This is because loss of contaminants from soils is often biphasic, whereby a short period of rapid dissipation is followed by a longer period of contaminant release. Dissipation processes, including leaching and volatilization, exhibit similar behavior. The primary rate-limiting factors governing this behavior are postulated to be fundamental sorption/ desorption mechanisms, including intraparticle diffusion, intrasorbent diffusion and chemisorption, which control the distribution of contaminant between the solid and aqueous or gaseous phases of soils and, hence, the supply of contaminant available to the various dissipation processes. In this article, we consider the relevance of biphasic desorption kinetics to existing soil-quality limits. We contend that the concentration of a given contaminant in a given soil when the “residual” phase of dissipation is reached represents an intrinsic kinetic constraint to the remediation of contaminated soil. Because of the effects of the primary rate-limiting mechanisms discussed above, it is unlikely that (in the absence of any engineering solution to the problem) any appreciable change in the contaminant concentration will occur over practical time scales under prevailing environmental conditions for a given soil. We define this contaminant concentration as a kinetically constrained soil quality limit (KCSQL) and apply it to selected examples of contaminant dissipation from the literature, including polychlorinated biphenyls, polynuclear aromatic hydrocarbons, industrial solvents, and pesticides in a range of soils. Finally, we examine the relationship between the derived KCSQLs and the Dutch “cleanup” values and soil-quality criteria adopted in other countries.

Environmental fate and effects of MCPA: A Canadian perspective

Abstract: A review of the environmental chemistry, fate, and toxicology of the herbicide MCPA was conducted. MCPA is used worldwide and is among the top ten herbicides sold in Canada. It has a systemic effect and is used to control a large range of broadleaf weeds in agricultural and noncrop lands. MCPA is highly water soluble and has a low affinity for most soil types, which gives it the potential to leach and contaminate groundwaters. It can undergo microbial degradation in aerobic conditions; therefore, it is only slightly persistent in soil and water. In Canada, MCPA has been detected in surface waters at levels varying between 0.00003 and 0.013 mg/l, and at relatively high levels in some groundwater (1.0 mg/1). It has also been reported to affect organisms such as the diatom Navicula pelliculosa at levels as low as of 0.026 mg/1, and the beagle dog at concentrations of 0.75 mg/kg/d. This review includes the development of the Canadian Water Quality Guidelines for MCPA, which are numerical concentratio...

Emulsion‐mediated transport of nonaqueous‐phase liquid in porous media: A review∗

Abstract: A review of literature on the formation, characteristic properties, and flow of emulsion in subsurface environment, and its potential impact on the transport of nonaqueous‐phase liquids (NAPLs) is provided. Synthesis of the literature indicates that emulsions can form during petroleum recovery as a result of production of natural surfactants by soil microorganisms, and the use of synthetic surfactants to clean up NAPL‐contaminated soils and aquifers. The use of surfactants as a remediation technique to remove hazardous NAPLs from soil and groundwater has been explored in some detail. However, cost‐effective and high‐efficiency remediation approaches using surfactants have yet to be accomplished. This review suggests that the use of surfactants to remove NAPLs from soil may involve the formation and flow of emulsions in the subsurface environment. The flow of emulsions may influence the transport of hazardous NAPLs in the subsurface environment, depending on the type and stability of emulsion form...

Reactor systems for microbial desulfurization of coal: an overview

Abstract: Precombustion microbial desulfurization of coal has significant advantages over physicochemical processes. Its application on a large scale is still in its infancy. The cost‐effectiveness of microbial coal desulfurization is dependent on the type of reactor system used. The technico‐economic feasibilities of various bioreactor systems, such as packed‐bed reactors, agitated aerated bioreactors, airlift recycle bioreactors, plug‐flow bioreactors, and continuous stirred‐tank reactors have been reviewed extensively. Few processes are also suggested for effective desulfurization of coal.