Contaminants Of Concern Research Articles

Soil gas gradient method for estimating natural source zone depletion rates of LNAPL and specific chemicals of concern

This paper presents a simplified approach for the soil gas gradient method for estimating natural source zone depletion (NSZD) rates of specific contaminants of concern (COCs) at sites contaminated by light non-aqueous phase liquids (LNAPL). Traditional approaches to quantify COC-specific NSZD rates often rely on numerical or analytical reaction-transport models that require detailed site-specific data. In contrast, the proposed method employs simple analytical solutions, making it more accessible to practitioners. Specifically, it requires only the maximum soil gas concentration, the effective diffusion coefficient, and the diffusive reaction length calculated from vertical soil gas concentration profiles. The simplified approach was validated against a reactive transport numerical model reported in the literature, showing consistent results within the same order of magnitude for BTEX NSZD rates at a gasoline spill site in South Carolina. Further validation using a larger dataset involved comparing NSZD rate estimates for benzene and total petroleum hydrocarbons (TPH) against those obtained using BioVapor, utilizing empirical soil gas data from the USEPA Petroleum Vapor Intrusion Database. Results demonstrated a strong correlation between NSZD rates and maximum soil gas concentrations, allowing the development of a rapid screening approach based only on the measured soil gas concentrations and literature values for diffusion coefficients and diffusive reaction lengths. This approach aligned well with previous modeling studies and was consistent with literature values for TPH NSZD rates. Overall, both the simplified and screening approaches offer practical, easy-to-use tools for evaluating temporal variability in natural attenuation rates, supporting baseline assessments and ongoing performance evaluations of remediation at LNAPL sites.

Teasing out the Effects of Natural Stressors at Chemically Contaminated Sites.

Aquatic ecosystems are often impacted by a multitude of stressors, many of which are introduced by a combination of anthropogenic activities such as agricultural development, urbanization, damming, and industrial discharge. Determining the primary stressors responsible for ecological impairments at a site can be complex and challenging; however, it is crucial for making informed management decisions. Improper diagnosis of an impaired system can lead to misguided attempts at remediation, which can be both time consuming and costly. We focused on the development, implementation, and evaluation of methodologies that, in combination, allowed us to identify the primary stressors. These included a four-phase, weight-of-evidence (WOE) assessment including in situ Toxicity Identification and Evaluation (iTIE) testing, physicochemical and macrobenthos characterization, reciprocal sediment transplants, and laboratory and in situ toxicity testing. The contaminants of concern (COCs) at the site were elevated levels of ammonia, chloride, pH, and total dissolved solids in groundwater upwellings into a high-quality waterway. Reciprocal transplants of site sediments and nearby reference sediments and traditional benthic sampling showed impaired benthic indices and multiple stations around a contaminated industrial settling basin. Impaired stations had elevated COCs in groundwaters but exhibited a steep vertical concentration gradient, with concentrations decreasing near the sediment-surface water interface. We describe Phase 4 of the study, which focused on teasing out the role of dissolved oxygen sags in benthic macroinvertebrate responses. Extensive submerged and emergent macrophytes, algae, and cyanobacteria co-occurred at the impaired sites and increased throughout the summer. Laboratory testing suggested that ammonia and pH were possibly toxic at the sites, based on groundwater concentrations. The in situ toxicity testing, however, showed toxicity occurring even at stations with low levels of COCs concurrently with large diurnal fluxes in dissolved oxygen (DO). A final phase using a type of iTIE approach utilized limnocorrals with and without aeration and with in situ toxicity measures using Hyalella azteca. The Phase 4 assessment revealed that low DO levels were primarily responsible for impaired benthic communities, and COC upwellings were diluted at the sediment-water interface to nontoxic levels. These findings will allow for improved management decisions for more efficient and effective restoration activities. Environ Toxicol Chem 2024;43:1524-1536. © 2024 SETAC.

Quantitative tracing the sources and human risk assessment of complex soil pollution in an industrial park

Pollution in industrial parks has long been characterized by complex pollution sources and difficulties in identifying pollutant origins. This study focuses on a typical industrial park consisting of 11 factories (F1–F11) including organic pigment, inorganic pigment, and chemical factories in Hunan Province, China, here, a total of 327 sample points were surveyed. Eight pollutants (Mn, Cd, As, Co, NH3–N, l, 1,2-Trichloroethane, chlorobenzene, and petroleum hydrocarbons) were classified as contaminants of concern (COCs). This study assessed the contributions of driving factors to the distribution of COCs in the soil. Pollutant source apportionment was conducted using positive matrix factorization (PMF) and random forest (RF). The results revealed that the main factors driving pollution are groundwater migration, non-compliant emissions, leaks during production, and interactions among pollutants. The primary pollution sources were four chemical factories and an inorganic pigment factory. Source 5 demonstrates significant correlations with TCA (29.6%), CB (30%), and As (31.6%). Two chemical factories (F7 and F10) are the most significant pollution source with a risk assessment contribution rate of more than 60%. The present study sheds some light on the contamination characteristics, source apportionment and source-health risk assessment of COCs in industrial park. By utilizing the proposed research framework, decision-makers can effectively prioritize and address identified pollution sources.

Formerly used defense sites on Unalaska Island, Alaska: Mapping a legacy of environmental pollution.

Unalaska Island, Alaska, served as a US military base during World War II. The military installed bases on Unalaska and nearby islands, many of which were built adjacent to Unangan communities. The military used toxic compounds in its operations and left a legacy of pollution that may pose health risks to residents and local wildlife. The goals of this study were to identify hotspots of contamination remaining at Unalaska formerly used defense (FUD) sites, evaluate the risk posed by arsenic, and examine "no US Department of Defense action indicated" (NDAI) status determinations for FUD sites near communities. We compiled soil chemistry data from remediation reports prepared by the US Army Corps of Engineers at 18 FUD sites on and near Unalaska. Nine had past and/or active remediation projects and on-site sampling data. Eight sites did not have sampling data and were characterized as NDAI. One site was listed as closed. For the nine sites with sampling data, we compiled data for 22 contaminants of concern (COC) and compared concentrations to soil cleanup levels for human health (18 AAC 75.341). We mapped contaminant concentrations exceeding these levels to identify hotspots of contamination. We found that concentrations of some of the 22 COC exceeded Alaska cleanup levels despite remediation efforts, including diesel range organics, arsenic, and lead. The highest COC concentrations were at the FUD site adjacent to the City of Unalaska. A quantitative risk assessment for arsenic found that the risk of exposure through drinking water is low. We highlight concerns with NDAI designations and current remedial practices at remote FUD sites located adjacent to communities. Our data suggest the need for further remediation and monitoring efforts on Unalaska for certain contaminants and research to examine potential threats to human and animal health associated with these sites. Integr Environ Assess Manag 2024;20:1420-1431. © 2024 SETAC.

Understanding RNG Gas Quality through Execution at Newtown Creek WRRF RNG

With each passing year a new record for global emissions is set (1) and policymakers and utility companies must embrace all avenues for decarbonization of energy. Universal adoption of electrification for every building and home by 2050 (2) is not practical, a balance must be struck between an equitable transition to cleaner energy supplies and ensuring uninterrupted, safe delivery of energy to utility customers. Renewable Natual Gas (RNG) is a molecule-for-molecule replacement of traditional geological natural gas with tangible life cycle emissions reductions. California continues to lead the way, initially starting with the low carbon fuel standard (LCFS) which aimed to reduce the carbon intensity of transportation fuel, and subsequently, Senate Bill 1440, which established RNG procurement goals including 12% RNG by 2030 (3). Other States are starting to adopt similar changes such as Oregon’s Senate Bill 98 and Colorado’s Senate Bill 21-264. As utilities attempt to transition the energy network, they must never compromise system safety and reliability. Recognizing that raw biogas has dangerous levels of contaminants of concern (COC) and must be conditioned to pipeline quality, its important utility companies better understand the methods with which methane is extracted and the testing protocols used to confirm performance. This paper highlights the equipment, processes, and testing regime National Grid and its partner the New York City Department of Environmental Protection (NYC DEP) deployed as part of its Newtown Creek RNG project, which successfully began injecting RNG into the NYC gas distribution network in October 2022.

Developmental exposure to corn grown on Lake Erie dredged material: a preliminary analysis.

While corn is considered to be a healthy food option, common agricultural practices, such as the application of soil amendments, might be introducing contaminants of concern (COC) into corn plants. The use of dredged material, which contain contaminants such as heavy metals, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), as a soil amendment is increasing. Contaminants from these amendments can accumulate in corn kernels harvested from plants grown on these sediments and potentially biomagnify in organisms that consume them. The extent to which secondary exposure to such contaminants in corn affect the mammalian central nervous system has been virtually unexplored. In this preliminary study, we examine the effects of exposure to corn grown in dredge amended soil or a commercially available feed corn on behavior and hippocampal volume in male and female rats. Perinatal exposure to dredge-amended corn altered behavior in the open-field and object recognition tasks in adulthood. Additionally, dredge-amended corn led to a reduction in hippocampal volume in male but not female adult rats. These results suggest the need for future studies examining how dredge-amended crops and/or commercially available feed corn may be exposing animals to COC that can alter neurodevelopment in a sex-specific manner. This future work will provide insight into the potential long-term consequences of soil amendment practices on the brain and behavior.

Management and Stimulation of High Metabolic Rates of Biomes to Effectively Remediate Mine Drainage

Drainages from mining operations frequently contain elevated levels of contaminants of concern (CoC). Indigenous adapted bacterial communities are characterized and the ability to reduce many CoC is showcased in different treatment implementations. Each contaminated site consists of a distinct prokaryotic community that in turn requires a specific C:N:P balanced environment to contribute to site remediation. This balanced bioremedial strategy is managed both for in situor fix-filmed bioreactors, using electron donor selection and ratios, redox potential, and hydraulic retention times. These communities can effectively treat elevated levels of hexavalent chromium (10 mg/L), nitrate (110 mg/L), and sulfate (1 250 mg/L) in a one-pot balanced system. Doi: 10.28991/HEF-2022-03-02-06 Full Text: PDF

Concentrations and fluxes of suspended particulate matter and associated contaminants in the Rhône River from Lake Geneva to the Mediterranean Sea

Abstract. The Rhône River is among the main rivers of western Europe and the biggest by freshwater discharge and sediment delivery to the Mediterranean Sea. Its catchment is characterized by distinct hydrological regimes that may produce annual sediment deliveries ranging from 1.4 to 18.0 Mt yr−1. Its course meets numerous dams, hydro and nuclear power plants as well as agricultural, urban and industrial areas. Moreover, with the climatic crisis we are currently facing, it is proven that the occurrence and the intensity of extreme events (floods or droughts) will increase. Therefore, it is crucial to monitor the concentrations and fluxes of suspended particulate matter (SPM) and associated contaminants to study the current trends and their evolution. In the Rhône River (from Lake Geneva to the Mediterranean Sea), a monitoring network of 15 stations (3 on the Rhône River and 12 on tributaries) has been set up in the past decade by the Rhône Sediment Observatory (OSR) to investigate the concentrations and the fluxes of SPM and associated contaminants as well as their sources. The main purpose of the OSR is to assess the long-term trend of the main contaminant concentrations and fluxes, and to understand their behavior during extreme events, such as floods or dam flushing operations. The dataset presented in this paper contains the concentrations and fluxes of SPM as well as the concentrations and fluxes of several particle-bound contaminants of concern, e.g., polychlorinated biphenyl (PCB), trace metal elements (TME) and radionuclides, the particle size distribution and the particulate organic carbon of SPM. Sediment traps or continuous flow centrifuges were used to collect sufficient amount of SPM in order to conduct the measurements, and data completion was applied to reconstruct missing values. This observatory is on-going since 2011 and the database is regularly updated. All the data are made publicly available in French and English through the BDOH OSR database at https://doi.org/10.15454/RJCQZ7 (Lepage et al., 2021).

Metallic Iron for Environmental Remediation: The Fallacy of the Electron Efficiency Concept

The suitability of remediation systems using metallic iron (Fe0) has been extensively discussed during the past 3 decades. It has been established that aqueous Fe0 oxidative dissolution is not caused by the presence of any contaminant. Instead, the reductive transformation of contaminants is a consequence of Fe0 oxidation. Yet researchers are still maintaining that electrons from the metal body are involved in the process of contaminant reduction. According to the electron efficiency concept, electrons from Fe0 should be redistributed to: i) contaminants of concern (COCs), ii) natural reducing agents (e.g., H2O, O2), and/or iii) reducible co-contaminants (e.g. NO3-). The electron efficiency is defined as the fraction of electrons from Fe0 oxidation which is utilized for the reductive transformations of COCs. This concept is in frontal contradiction with the view that Fe0 is not directly involved in the process of contaminant reduction. This communication recalls the universality of the concept that reductive processes observed in remediation Fe0/H2O systems are mediated by primary (e.g., FeII, H/H2) and secondary (e.g., Fe3O4, green rusts) products of aqueous iron corrosion. The critical evaluation of the electron efficiency concept suggests that it should be abandoned. Instead, research efforts should be directed towards tackling the real challenges for the design of sustainable Fe0-based water treatment systems based on fundamental mechanisms of iron corrosion.

Physical, chemical and toxicological properties of polycyclic aromatic hydrocarbons (PAHs) in human exposure assessments to contaminated soil and groundwater

Polycyclic aromatic hydrocarbons (PAHs) are a class of chemical substances consisting of carbon and hydrogen only, which have multiple fused ring systems. Although PAHs are widely recognised as contaminants of concern (CoC), no applicable limits have been established for groundwater in the Romanian legislation. Furthermore, the existing methodologies do not include guidelines for assessing the human exposure to contaminated soil and groundwater. The current research aims at identifying the relevant physical, chemical and toxicological properties of PAHs when conducting human exposure assessments for contaminated and potentially contaminated sites. The methods applied in the research are based on the general geoenvironmental risk assessment procedure by analysing the sources potentially generating PAHs, the migration and exposure pathway depending on their fate and transport properties, and the vulnerability to PAHs of the potential receptors, based on their toxicological profile.

Delineation of soil contaminant plumes at a co-contaminated site using BP neural networks and geostatistics

The delineation of contamination at a co-contaminated site is vital for designing remedial strategy and estimating costs. Backpropagation (BP) neural networks and the Nemerow pollution index (NPI) with 3-D kriging were combined in this study to delineate contaminant plumes, analyze the spatial distribution of pollutants in different layers and visualize them in three dimensions, quantify polluted areas and pollution levels, and identify hotspots of the contaminants of concern (COCs). The results of a comprehensive assessment performed using BP networks and NPI were compared. The analysis of the volumes of soil contaminated with specific COCs in different soil layers showed that arsenic (As) hardly migrated downgradient whereas benzo[a]pyrene (BaP) had a strong tendency to migrate. The tendency of fluorene (FLE), naphthalene (NAP), and phenanthrene (PHE) to migrate was between that for As and BaP. The volumes of earth contaminated with of all five of these COCs generally decreased with increasing pollution levels. The volumes of PHE, FLE, and NAP at different pollution levels exhibited similar trends, and most contaminated areas were safe. The volume of BaP at high pollution levels was markedly greater than that for the other four COCs, and the volume of As at low pollution levels was also notably greater than that for the other four pollutants. (3) The spatial patterns performed by the NPI and BP network comprehensive assessment methods were similar. However, BP networks can overcome the deficiencies of NPI, which are amplification of the effect of heavily polluted elements and narrowing the separability of polluted and unpolluted areas. After comparing performance and performing a cost-benefit analysis, we propose a model that integrates BP networks and geostatistics to delineate soil contaminant plumes at co-contaminated sites.

Association between elevated placental polycyclic aromatic hydrocarbons (PAHs) and PAH-DNA adducts from Superfund sites in Harris County, and increased risk of preterm birth (PTB)

The preterm birth (PTB) rate in Harris County, Texas, exceeds the U.S. rate (11.4% vs.9.6%), and there are 15 active Superfund sites in Harris County. Polycyclic aromatic hydrocarbons (PAHs) are contaminants of concern (COC) at Superfund sites across the nation. In this investigation, we tested the hypothesis that higher levels of exposure to PAHs and PAH-DNA adducts in placenta of women living near Superfund sites contribute to the increased rate of PTBs. Levels of benzo[a]pyene (BP), benzo[b]fluorene (BbF) and dibenz[a,h]anthracene (DBA), were higher in placentae from preterm deliveries compared with term deliveries in women living near Superfund sites, whereas this was not the case for women living in non-Superfund site areas. Among the PAHs, DBA levels were significantly higher than BP or BbF, and DBA levels were inversely correlated with gestational age at delivery and birth weight. Bulky PAH-DNA adducts are more prevalent in placental tissue from individuals residing near Superfund sites. Expression of Ah receptor (AHR) and NF-E2-related factor 2 (NRF2) was decreased in preterm deliveries in subjects residing near Superfund sites. Unbiased metabolomics revealed alterations in pathways involved in pentose phosphate, inositol phosphate and starch and sucrose metabolism in preterm subjects in Superfund site areas. In summary, this is the first report showing an association between PAH levels, DNA adducts, and modulation of endogenous metabolic pathways with PTBs in subjects residing near Superfund sites, and further studies could lead to novel strategies in the understanding of the mechanisms by which PAHs contribute to PTBs in women.

Assessment of legacy and emerging contaminants in an introduced catfish and implications for the fishery.

Since introduction into the Chesapeake Bay watershed in the 1970s, blue catfish (Ictalurus furcatus) populations have increased, impacting native species. One strategy suggested to limit their growing numbers is to expand the existing commercial fishery. However, the promotion of human consumption of this large, omnivorous fish may increase exposure to contaminants of concern (COC). However, there are few published data on contaminants in blue catfish. To evaluate this possibility, we measured COC (PCBs, PBDEs, OCs, Hg) in individual fillets and compared levels to established consumption advisory limits. James River (near Richmond, Virginia) and Upper Potomac River (downstream of Washington DC) fish exhibited higher burdens of most COC than those from the lower James and rural Rappahannock rivers. Fish sex and δ15N values (surrogate for trophic position) did not correlate with COC concentrations. Potomac River fish exhibited greatest δ15N, perhaps related to local wastewater inputs. Despite differences in human population densities among watersheds, fish mercury (Hg) levels were similar. Most fillets surpassed US EPA advisory limits for unrestricted consumption (> 16 meals/month) for Hg and PCBs. Hg and PCB advisories in the region typically restrict consumption to two 220g meals/month. Hence, individuals who rely on fish for a large portion of their diet may be exposed to unacceptable Hg and PCB concentrations. COC levels typically increased with fish length; in particular, fish > 550mm often exceeded unrestricted consumption limits for chlordanes and DDTs. PBDEs, pentachloroanisole, hexachlorobenzene, and mirex levels were generally below established advisories. However, because fish advisories are based on the expected consequences from single contaminants and a single or limited number of toxicological endpoints, consumers face greater risks due to cumulative effects from all coincident COCs, as well as additional exposure pathways, such as other food and air. The additional data on contaminant levels reported here will increase the accuracy of forecasted risks. However, it also illustrates the complexity in communicating the risks from multi-contaminant exposure.

Recent Trends in the Selection of Remedies for Groundwater, Soil, and Sediment at Superfund Sites

Recent Trends in the Selection of Remedies for Groundwater, Soil, and Sediment at Superfund Sites

Performance evaluation of an in situ source area combined remedy for the remediation of commingled chlorinated ethanes and ethenes

AbstractThe chlorinated volatile organic compounds (CVOCs), tetrachloroethene (PCE), trichloroethene (TCE), and 1,1,1‐trichloroethane (1,1,1‐TCA), often found as commingled contaminants of concern (COCs) in groundwater, can degrade via a variety of biotic and abiotic reductive pathways. In situ remediation of a groundwater contaminant source area containing commingled 1,1,1‐TCA, PCE, and TCE was conducted using a combined remedy/treatment train approach. The first step was to create geochemically reducing conditions in the source area to degrade the CVOCs to lesser chlorinated CVOCs (i.e., 1,1‐dichloroethane [1,1‐DCA], 1,1‐dichlorethene [1,1‐DCE], cis‐1,2‐dichoroethene [cis‐1,2‐DCE], and vinyl chloride [VC]) via enhanced reductive dechlorination (ERD). Carbon substrates were injected to create microbial‐induced geochemically reducing conditions. An abiotic reductant (zero‐valent iron [ZVI]) was also used to further degrade the CVOCs, minimizing the generation of 1,1‐DCE and VC, and co‐precipitate temporarily mobilized metals. An in situ aerobic zone was created downgradient of the treatment zone through the injection of oxygen. Remaining CVOC degradation products and temporarily mobilized metals (e.g., iron and manganese) resulting from the geochemically reducing conditions were then allowed to migrate through the aerobic zone. Within the aerobic zone, the lesser chlorinated CVOCs were oxidized and the solubilized metals were precipitated out of solution. The injection of a combination of carbon substrates and ZVI into the groundwater system at the site studied herein resulted in the generation of a geochemically reducing subsurface treatment zone that has lasted for more than 4.5 years. Mass concentrations of total CVOCs were degraded within the treatment zone, with near complete transformation of chlorinated ethenes and a more than 90 percent reduction of CVOC mass concentrations. Production of VC and 1,1‐DCE has been minimized through the combined effects of abiotic and biological processes. CVOC concentrations have declined over time and temporarily mobilized metals are precipitating out of the dissolved phase. Precipitation of the dissolved metals was mitigated using the in situ oxygenation system, also resulting in a return to aerobic conditions in downgradient groundwater. Chloroethane (CA) is the dominant CVOC degradation product within the treatment zone and downgradient of the treatment zone, and it is expected to continue to aerobically degrade over time. CA did not accumulate within and near the aerobic oxygenation zone. The expectations for the remediation system are: (1) the concentrations of CVOCs (primarily in the form of CA) will continue to degrade; (2) total organic carbon concentrations will continue to decline to pre‐remediation levels; and, (3) the groundwater geochemistry will experience an overall trend of transitioning from reducing back to pre‐remediation mildly oxidizing conditions within and downgradient of the treatment zone.

OPERATIONALIZING PHYTOREMEDIATION: BEST MANAGEMENT PRACTICES

Introduction For at least three decades, plants and their associated microbes have been experimentally shown to extract, degrade and volatilize some contaminants of concern (CoC). But the greater promise of phytoremediation to be used widely and effectively has yet to be realized. One of the principal reasons is the gap between experimental and operational applications. Without effective operationalization, many projects fail and confidence is lost in the efficacy of the technology. Several obstacles have materialized in the process of commercializing phytoremediation that have prevented this technology from being widely adopted: lack of field-based research on techniques; lack of qualified persons for design, installation and management; and few incentives to share BMPs among commercial providers. Each will be discussed below. Operational guidelines and best management practices (BMPs) are presented based on 18 years of experience on 20 different phytoremediation projects in Canada and Northeast US, on p...

In situ stabilization of NAPL contaminant source-zones as a remediation technique to reduce mass discharge and flux to groundwater

Widely used flushing and in-situ destruction based remediation techniques (i.e. pump-and treat, enhanced-solubilization, and chemical oxidation/reduction) for sites contaminated by nonaqueous phase liquid (NAPL) contaminant sources have been shown to be ineffective at complete mass removal and reducing aqueous-phase contaminant of concern (COC) concentrations to levels suitable for site closure. A remediation method was developed to reduce the aqueous solubility and mass-flux of COCs within NAPL through the in-situ creation of a NAPL mixture source-zone. In contrast to remediation techniques that rely on the rapid removal of contaminant mass, this technique relies on the stabilization of difficult-to-access NAPL sources to reduce COC mass flux to groundwater. A specific amount (volume) of relatively insoluble n-hexadecane (HEXDEC) or vegetable oil (VO) was injected into a trichloroethene (TCE) contaminant source-zone through a bench-scale flow cell port (i.e. well) to form a NAPL mixture of targeted mole fraction (TCE:HEXDEC or TCE:VO). NAPL-aqueous phase batch tests were conducted prior to the flow-cell experiments to evaluate the effects of various NAPL mixture ratios on equilibrium aqueous-phase concentrations of TCE to design optimal NAPL (HEXDEC or VO) injection volumes for the flow-cell experiments. The NAPL-stabilization flow-cell experiments initiated and sustained significant reductions in COC concentration and mass flux due to a combination of both reduced relative permeability (increased NAPL-saturation) and via modification of NAPL composition (decreased TCE mole fraction). Variations in remediation performance (i.e. impacts on TCE concentration and mass flux reduction) between the different HEXDEC injection volumes were relatively minor, and therefore inconsistent with Raoult's Law predictions. This phenomenon likely resulted from non-uniform mixing of the injected HEXDEC with TCE in the source-zone. VO injection caused TCE concentrations and mass-flux to decrease more rapidly than with HEXDEC injections. This phenomenon occurred because the injected VO was observed to mix more uniformly with TCE in the source-zone due to a lower mobilization potential. The relative lower density differences (buoyancy effects) between VO and the flushing solution (water) was the primary factor contributing to the lower mobilization potential for VO. Overall, this study indicated that the delivery of HEXDEC or VO into the toxic TCE source-zone was effective in significantly reducing contaminant aqueous-phase concentration and mass-flux. However, the effectiveness of this in-situ NAPL stabilization technique depends on source delivery, uniform mixing of amendment, and that the amendment remains immobilized within and around the NAPL contaminant source.

System-Dynamics Modeling of Source Mass-Depletion and Risk- Exposure Evolution for Natural Attenuation Processes in the Vadose Zone

Public health is potentially at risk after a contaminant of concern (COC) is released into the ecosphere. The extent of contamination depends on numerous factors; modeling a contaminant’s dynamic behavior is challenging, given the multitude of relevant parameters and the fluid nature of processes involved. For example, weather events (e.g., wet or dry periods) may affect the mass depletion and the fate and transport of COCs, and hence, the risk assessment of current and potential future exposures. Thus, to give realistic estimates for potential risks, a contaminant’s dynamic behavior must be taken into account in decision-making processes. In this paper, a system-dynamics framework for a dynamic-risk assessment is developed taking into consideration the mass-depletion processes in a natural attenuation environment. This framework rests on the premise that natural attenuation is a complex system involving a variety of source mass-depletion phenomena which evolve over time. Through cause-and-effect loops, a system-dynamics model connects the contaminant’s physicochemical and biological mass-depletion processes with the potential risk for exposure by water ingestion and air inhalation. The model considers an idealistic approach involving a continuous average infiltration rate, and a realistic approach incorporating weather fluctuations into the system. To test the proposed model, a conceptual example of benzene contamination in the vadose zone is analyzed. Geological site specifications, contaminant characteristics, and fate-and-transport mechanisms contributing to source mass-depletion are considered, including water infiltration, volatilization, biodegradation, and groundwater recharge. Cancer risk is assessed in two exposure routes (ingestion, inhalation) for idealistic and realistic case scenarios.

Accumulation of Heavy Metal Ions by Eichhornia Crassipes from Battery Industry Effluent under the Influence of Cattle Manure

Phytoremediation, an emerging technology which uses plants to remove contaminants of concern (COC) such as organic and inorganic compounds especially heavy metals (HM). The present study focuses on assessing the toxicity of heavy metals available in effluents discharged from industries and the accumulation ability of an aquatic plant, Eichhornia crassipes (water hyacinth). Phytoremedial potential of E. Crassipes and HM interaction between soil and water were evaluated in the present study under the presence of cow dung manure as an enhancer. Heterogenous accumulation of metal ions were found in the plant. Heavy metal concentration in plant parts were varied for roots and shoots. The concentration of HM ions in the plant parts were varied from root to shoot. Value of translocation factor (TF) was found to be in the region 0.5 – 0.8, with Fe has low (0.51) and Pb has high (0.77), bioconcentration factor (BCF) were in the order of Ar > Ca > Zn > Fe > Pb at both roots and shoots. Transposition factor (TrF) of all HM ions were >1.5 except for Zn (1.21). E. Crassipes was found to accumulate a large amount of HM ions and could be used for efficient treatment of contaminated water.

In situ solidification and in situ chemical oxidation combined in a single application to reduce contaminant mass and leachability in soil

A contaminated soil was treated in the laboratory with in situ chemical oxidation and in situ solidification/stabilization combined in a single application. Portland cement can activate the persulfate anion (S2O82−) in sodium persulfate (Na2S2O8), chemically oxidizing organic contaminants. Ten doses of Na2S2O8, ranging from 0.25% to 5% (by weight) with a cement:Na2S2O8 ratio of 2:1, completely activated S2O82− within 2.5h of mixing. Chemical oxidation removed a significant portion of the contaminants of concern (COCs), including BTEX, naphthalene, and 17 higher molecular weight PAHs. COC oxidation showed saturation-type dose-response curves, with pronounced contaminant removal at Na2S2O8 doses below 1.5%, and little removal at higher doses. Plots of reduced COC leachability vs. cement dose for combined oxidation and stabilization treatments were similar to those for COC oxidation, but for stabilization treatments the dose-response was roughly linear, and inversely related to the molecular weight of the COCs. Even with low Na2S2O8 doses, combined oxidation and stabilization treatments reduced COC leachability far more than stabilization treatments alone using the same PC dose, because of the COC removal achieved by Na2S2O8 oxidation. The increase in soil strength and decrease in hydraulic conductivity were unaffected by Na2S2O8.