A study of chlorinated solvent contamination of the aquifers of an industrial area in central Italy: a possibility of bioremediation

Field test of a bioaugmentation agent for the bioremediation of chlorinated ethene contaminated sites

Chlorinated ethenes are toxic compounds that were widely used in the past, and their improper handling and storage caused notable pollutions worldwide. In situ bioremediation by reductive dechlorination of bacteria is a cost-effective and ecologically friendly way to eliminate these pollutions. During the present study, the efficiency of a previously developed bioaugmentation agent combined with biostimulation was tested under field conditions in contaminated soil. Furthermore, the preservation of dechlorinating ability was also investigated in a long-term experiment. Initially, aerobic conditions were present in the groundwater with possible presence of anaerobic micro-niches providing habitat for Brocadia related anammox bacteria. "Candidatus Omnitrophus" was also identified as a dominant member of community then. Significant changes were detected after the biostimulation, anaerobic conditions established and most of the dominant OTUs were related to fermentative taxa (e.g. Clostridium, Trichococcus and Macillibacteroides). Dominant presence of vinyl-chloride coupled with the lack of vinyl-chloride reductase gene was observed. The most notable change after the bioaugmentation was the significant decrease in the pollutant quantities and the parallel increase in the vcrA gene copy numbers. Similar to post-biostimulation state, fermentative bacteria dominated the community. Bacterial community composition transformed considerably with time after the treatment, dominance of fermentative-mainly Firmicutes related-taxa decreased and chemolithotrophic bacteria became abundant, but the dechlorinating potential of the community remained and could be induced by the reappearance of the pollutants even after 4 years.

Pilot tests for the optimization of the bioremediation strategy of a multi-layered aquifer at a multi-focus site impacted with chlorinated ethenes

A multi-layered aquifer in an industrial area in the north of the Iberian Peninsula is severely contaminated with the chlorinated ethenes (CEs) tetrachloroethylene, trichloroethylene, cis-1,2-dichloroethylene, and vinyl chloride. Both shallow and deep aquifers are polluted, with two differentiated north and south CEs plumes. Hydrogeochemical and isotopic data (δ13C of CEs) evidenced natural attenuation of CEs. To select the optimal remediation strategy to clean-up the contamination plumes, laboratory treatability studies were performed, which confirmed the intrinsic biodegradation potential of the north and south shallow aquifers to fully dechlorinate CEs to ethene after injection of lactate, but also the combination of lactate and sulfidized mZVI as an alternative treatment for the north deep aquifer. In the lactate-amended microcosms, full dechlorination of CEs was accompanied by an increase in 16S rRNA gene copies of Dehalococcoides and Dehalogenimonas, and the tceA, vcrA and bvcA reductive dehalogenases. Three in situ pilot tests were implemented, which consisted in injections of lactate in the north and south shallow aquifers, and injections of lactate and sulfidized mZVI in the north deep aquifer. The hydrogeochemical, isotopic and molecular analyses used to monitor the pilot tests evidenced that results obtained mimicked the laboratory observations, albeit at different dechlorination rates. It is likely that the efficiency of the injections was affected by the amendment distribution. In addition, monitoring of the pilot tests in the shallow aquifers showed the release of CEs due to back diffusion from secondary sources, which limited the use of isotopic data for assessing treatment efficiency. In the pilot test that combined the injection of lactate and sulfidized mZVI, both biotic and abiotic pathways contributed to the production of ethene. This study demonstrates the usefulness of integrating different chemical, isotopic and biomolecular approaches for a more robust selection and implementation of optimal remediation strategies in CEs polluted sites.

Evaluating groundwater ecosystem dynamics in response to post in-situ remediation of mixed chlorinated volatile organic compounds (CVOCs): An insight into microbial community resilience, adaptability, and metabolic functionality for sustainable remediation and ecosystem restoration

The in-situ remediation of groundwater contaminated with mixed chlorinated volatile organic compounds (CVOCs) has become a significant global research interest. However, limited attention has been given in understanding the effects of these remediation efforts on the groundwater microbial communities, which are vital for maintaining ecosystem health through their involvement in biogeochemical cycles. Hence, this study aimed to provide valuable insights into the impacts of in-situ remediation methods on groundwater microbial communities and ecosystem functionality, employing high-throughput sequencing coupled with functional and physiological assays. The results showed that both bioremediation and chemical remediation methods adversely affected microbial diversity and abundance compared to non-polluted sites. Certain taxa such as Pseudomonas, Acinetobacter, and Vogesella were sensitive to these remediation methods, while Aquabacterium exhibited greater adaptability. Functional annotation unveiled the beneficial impact of bioremediation on the sulfur cycle and specific taxa such as Cellvibrio, Massilia, Algoriphagus, and Flavobacterium which showed a significant positive relationship with dark oxidation of sulfur compounds. In contrast, chemical remediation showed adverse impacts on the nitrogen cycle with a reduced abundance of nitrogen and nitrate respiration along with a reduced utilization of amines (nitrogen rich substrate). The findings of this study offer valuable insights into the potential impacts of in-situ remediation methods on groundwater microbial communities and ecosystem functionality, emphasizing the need for meticulous consideration to ensure the implementation of effective and sustainable remediation strategies that safeguard ecosystem health and function.

Biodegradation of chloroethene compounds under microoxic conditions

The biodegradation of chloroethene compounds under oxic and anoxic conditions is well established. However, the biological reactions that take place under microoxic conditions are unknown. Here, we report the biostimulated (BIOST: addition of lactate) and natural attenuated (NAT) degradation of chloroethene compounds under microoxic conditions by bacterial communities from chloroethene compounds-contaminated groundwater. The degradation of tetrachloroethene was significantly higher in NAT (15.14% on average) than in BIOST (10.13% on average) conditions at the end of the experiment (90 days). Sporomusa, Paracoccus, Sedimentibacter, Pseudomonas, and Desulfosporosinus were overrepresented in NAT and BIOST compared to the source groundwater. The NAT metagenome contains phenol hydrolase P1 oxygenase (dmpL), catechol-1,2-dioxygenase (catA), catechol-2,3-dioxygenases (dmpB, todE, and xylE) genes, which could be involved in the cometabolic degradation of chloroethene compounds; and chlorate reductase (clrA), that could be associated with partial reductive dechlorination of chloroethene compounds. Our data provide a better understanding of the bacterial communities, genes, and pathways potentially implicated in the reductive and cometabolic degradation of chloroethene compounds under microoxic conditions.

Alleviating Chlorinated Alkane Inhibition on Dehalococcoides to Achieve Detoxification of Chlorinated Aliphatic Cocontaminants

Cocontamination by multiple chlorinated solvents is a prevalent issue in groundwater, presenting a formidable challenge for effective remediation. Despite the recognition of this issue, a comprehensive assessment of microbial detoxification processes involving chloroethenes and associated cocontaminants, along with the underpinning microbiome, remains absent. Moreover, strategies to mitigate the inhibitory effects of cocontaminants have not been reported. Here, we revealed that chloroform exhibited the most potent inhibitory effects, followed by 1,1,1-trichloroethane and 1,1,2-trichloroethane, on dechlorination of dichloroethenes (DCEs) in Dehalococcoides-containing consortia. The observed inhibition could be attributed to suppression of biosynthesis and enzymatic activity of reductive dehalogenases and growth of Dehalococcoides. Notably, cocontaminants more profoundly inhibited Dehalococcoides populations harboring the vcrA gene than those possessing the tceA gene, thereby explaining the accumulation of vinyl chloride under cocontaminant stress. Nonetheless, we successfully ameliorated cocontaminant inhibition by augmentation with Desulfitobacterium sp. strain PR owing to its ability to attenuate cocontaminants, resulting in concurrent detoxification of DCEs, trichloroethanes, and chloroform. Microbial community analyses demonstrated obvious alterations in taxonomic composition, structure, and assembly of the dechlorinating microbiome in the presence of cocontaminants, and introduction of strain PR reshaped the dechlorinating microbiome to be similar to its original state in the absence of cocontaminants. Altogether, these findings contribute to developing bioremediation technologies to clean up challenging sites polluted with multiple chlorinated solvents.

A deep continental aquifer downhole sampler for microbiological studies

To be effective, microbiological studies of deep aquifers must be free from surface microbial contaminants and from infrastructures allowing access to formation water (wellheads, well completions). Many microbiological studies are based on water samples obtained after rinsing a well without guaranteeing the absence of contaminants from the biofilm development in the pipes. The protocol described in this paper presents the adaptation, preparation, sterilization and deployment of a commercial downhole sampler (PDSshort, Leutert, Germany) for the microbiological studying of deep aquifers. The ATEX sampler (i.e., explosive atmospheres) can be deployed for geological gas storage (methane, hydrogen). To validate our procedure and confirm the need to use such a device, cell counting and bacterial taxonomic diversity based on high-throughput sequencing for different water samples taken at the wellhead or at depth using the downhole sampler were compared and discussed. The results show that even after extensive rinsing (7 bore volumes), the water collected at the wellhead was not free of microbial contaminants, as shown by beta-diversity analysis. The downhole sampler procedure was the only way to ensure the purity of the formation water samples from the microbiological point of view. In addition, the downhole sampler allowed the formation water and the autochthonous microbial community to be maintained at in situ pressure for laboratory analysis. The prevention of the contamination of the sample and the preservation of its representativeness are key to guaranteeing the best interpretations and understanding of the functioning of the deep biosphere.

Microbial Degradation of Rubber: Actinobacteria

Rubber is an essential part of our daily lives with thousands of rubber-based products being made and used. Natural rubber undergoes chemical processes and structural modifications, while synthetic rubber, mainly synthetized from petroleum by-products are difficult to degrade safely and sustainably. The most prominent group of biological rubber degraders are Actinobacteria. Rubber degrading Actinobacteria contain rubber degrading genes or rubber oxygenase known as latex clearing protein (lcp). Rubber is a polymer consisting of isoprene, each containing one double bond. The degradation of rubber first takes place when lcp enzyme cleaves the isoprene double bond, breaking them down into the sole carbon and energy source to be utilized by the bacteria. Actinobacteria grow in diverse environments, and lcp gene containing strains have been detected from various sources including soil, water, human, animal, and plant samples. This review entails the occurrence, physiology, biochemistry, and molecular characteristics of Actinobacteria with respect to its rubber degrading ability, and discusses possible technological applications based on the activity of Actinobacteria for treating rubber waste in a more environmentally responsible manner.

Systematical exploration of the common solvent toxicity at whole organism level by behavioral phenomics in adult zebrafish

Common solvents are frequently used as carriers to dissolve chemicals with a hydrophobic property that is extensively applied in the industrial and biomedical fields. In this study, we aimed to systematically study the sub-chronic effect of ten common solvents at low concentration exposure in adult zebrafish and perform neurobehavioral assessments for mechanistic exploration. After exposed to ten common solvents, including methanol, ethanol (EtOH), dimethyl sulfoxide (DMSO), isopropanol, acetone, polyethylene glycol-400 (PEG-400), glycerol, butanol, pentane, and tetrahydrofuran for continuous 10 day at 0.1% concentration level, adult zebrafish were subjected to perform a serial of behavioral tests, such as novel tank, mirror biting, predator avoidance, social interaction and shoaling. Later, 20 behavioral endpoints obtained from these five tests were transformed into a scoring matrix. Principal component analysis (PCA) and hierarchy clustering were performed to evaluate and compare the zebrafish behavior profiling. By using this phenomic approach, we were able to systematically evaluate the toxicity of the common solvents in zebrafish at a neurobehavioral level for the first time and found each common solvent-induced unique behavioral alteration to produce fingerprint-like patterns in hierarchy clustering and heatmap analysis. Among all tested common solvents, acetone and PEG-400 displayed better biocompatibility and less toxicity since they triggered less behavioral and biochemical alterations while methanol and DMSO caused severe behavior alterations in zebrafish after chronic exposure of these solvents. We conclude the behavioral phenomic approach conducted in this study providing a powerful tool to a systematical exploration of the common solvent toxicity at the whole organism level.

Effects of non-halogenated solvent on the main properties of a solution-processed polymeric thin film for photovoltaic applications: a computational study

Organic photovoltaic (OPV) devices have reached high power conversion efficiencies, but they are usually processed using halogenated toxic solvents. Hence, before OPV devices can be mass-produced by industrial processing, it would be desirable to replace those solvents with eco-friendly ones. Theoretical tools may be then a powerful ally in the search for those new solvents. In order to better understand the mechanisms behind the interaction between solvent and polymer, classical molecular dynamics (MD) calculations were used to produce a thin film of poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl) (PTB7-Th), processed using two different solvents. PTB7-Th is widely applied as a donor material in OPVs. The first solvent is ortho-dichlorobenzene (o-DCB), which is a highly toxic solvent widely used in lab-scale studies. The second solvent is ortho-methylanisole (o-MA), which is an eco-friendly solvent for organic photovoltaic (OPV) manufacturing. Here we use a solvent evaporation protocol to simulate the formation of the PTB7-Th film. We demonstrate that our theoretical MD calculations were able to capture some differences in the macroscopic properties of thin films formed by o-DCB or o-MA evaporation. We found that the interaction of the halogenated solvent with the polymer tends to break the bonds between the lateral thiophenediyl groups and the main chain. We show that those defects may create traps that can affect the charge transport and also can be responsible for a blue shift in the absorption spectrum. Using the Monte Carlo method, we also verified the influence of the resulting MD morphology on the mobility of holes. Our theoretical results showed good agreement with the experimental measurements and both demonstrate that o-MA can be used to make polymer thin films without any loss of key properties for the device performance. The findings here highlight the importance of theoretical results as a guide to the morphological optimization of green processed polymeric films.

Molecular mechanisms in phytoremediation of environmental contaminants and prospects of engineered transgenic plants/microbes

Concerns about emerging environmental contaminants have been growing along with industrialization and urbanization around the globe. Among various options for remediating these contaminants, phytotechnology is suggested as a feasible option to maintain the environmental sustainability. The recent advances in phytoremediation, genetic/molecular/omics/metabolic engineering, and nanotechnology are opening new paths for efficient treatment of emerging organic/inorganic contaminants. In this respect, elucidation of molecular mechanisms and genetic engineering of hyperaccumulator plants is expected to enhance remediation of environmental contaminants. This review was organized to offer valuable insights into the molecular mechanisms of phytoremediation and the prospects of transgenic hyperaccumulators with enhanced stress tolerance to diverse contaminants such as heavy metals and metalloids, xenobiotics, explosives, poly aromatic hydrocarbons (PAHs), petroleum hydrocarbons, pesticides, and nanoparticles. The roles of genoremediation and nanoparticles in augmenting the phytoremediation technology are also described in an interrelated framework with biotechnological prospects (e.g., plant molecular nano-farming). Finally, political debate on the preferential use of crops versus non-crop hyperaccumulators in genoremediation, limitations of transgenics in phytotechnologies, and their public acceptance issues are discussed in the policy framework.

Enhancement of Chromium (VI) Reduction in Microcosms Amended with Lactate or Yeast Extract: A Laboratory-Scale Study

A laboratory-scale study was carried out to evaluate the groundwater bioremediation potential of hexavalent chromium (Cr(VI)), taking into account the chromate pollution of an industrial site located in Southern Italy (Apulia Region). The reduction of Cr(VI) was studied on laboratory microcosms, set up in different experimental conditions, namely: ABIO (soil and water sterilized), BIO (soil and water not sterilized), LATT (with the addition of lactate), and YE (with the addition of yeast extract). Control test lines, set up by using sterilized matrices and amendments, were employed to assess the occurrence of the pollutant reduction via chemical processes. By combining molecular (microbial abundance, specific chromate reductase genes (ChR) and the Shewanella oinedensis bacterial strain) with chemical analyses of chromium (VI and III) in the matrices (water and soil) of each microcosm, it was possible to investigate the response of microbial populations to different experimental conditions, and therefore, to assess their bioremediation capability in promoting Cr(VI) reduction. The overall results achieved within this work evidenced the key role of amendments (lactate and yeast extract) in enhancing the biological reduction of hexavalent chromium in the contaminated aqueous phase of laboratory microcosms. The highest value of Cr(VI) removal (99.47%) was obtained in the YE amended microcosms at seven days.

Integrative isotopic and molecular approach for the diagnosis and implementation of an efficient in-situ enhanced biological reductive dechlorination of chlorinated ethenes

Based on the previously observed intrinsic bioremediation potential of a site originally contaminated with perchloroethene (PCE), field-derived lactate-amended microcosms were performed to test different lactate isomers and concentrations, and find clearer isotopic and molecular parameters proving the feasibility of an in-situ enhanced reductive dechlorination (ERD) from PCE-to-ethene (ETH). According to these laboratory results, which confirmed the presence of Dehalococcoides sp. and the vcrA gene, an in-situ ERD pilot test consisting of a single injection of lactate in a monitoring well was performed and monitored for 190 days. The parameters used to follow the performance of the ERD comprised the analysis of i) hydrochemistry, including redox potential (Eh), and the concentrations of redox sensitive species, chlorinated ethenes (CEs), lactate, and acetate; ii) stable isotope composition of carbon of CEs, and sulphur and oxygen of sulphate; and iii) 16S rRNA gene sequencing from groundwater samples. Thus, it was proved that the injection of lactate promoted sulphate-reducing conditions, with the subsequent decrease in Eh, which allowed for the full reductive dechlorination of PCE to ETH in the injection well. The biodegradation of CEs was also confirmed by the enrichment in ¹³C and carbon isotopic mass balances. The metagenomic results evidenced the shift in the composition of the microbial population towards the predominance of fermentative bacteria. Given the success of the in-situ pilot test, a full-scale ERD with lactate was then implemented at the site. After one year of treatment, PCE and trichloroethene were mostly depleted, whereas vinyl chloride (VC) and ETH were the predominant metabolites. Most importantly, the shift of the carbon isotopic mass balances towards more positive values confirmed the complete reductive dechlorination, including the VC-to-ETH reaction step. The combination of techniques used here provides complementary lines of evidence for the diagnosis of the intrinsic biodegradation potential of a polluted site, but also to monitor the progress, identify potential difficulties, and evaluate the success of ERD at the field scale.

A review of threats to groundwater quality in the anthropocene

Awareness concerning sustainable groundwater consumption under the context of land use and climate change is gaining traction, raising the bar for adequate understanding of the complexities of natural and anthropogenic processes and how they affect groundwater quality. The heterogeneous characteristics of aquifers have hampered comprehensive source, transport and contaminant identification. As questions remain about the behavior and prediction of well-known groundwater contaminants, new concerns around emerging contaminants are on the increase. This review highlights some of the key contaminants that originate from anthropogenic activities, organized based on land use categories namely agricultural, urban and industrial. It further highlights the extensive overlap, in terms of both provenance as well as contaminant type, between the different land use sectors. A selection of case studies from literature that describe the continued concern of established contaminants, as well as new and emerging compounds, are presented to illustrate the many qualitative threats to global groundwater resources. In some cases, the risk of groundwater contamination lacks adequate gravity, while in others the underlying physical and societal processes are not fully understood and activities may commence without adequately considering potential impacts. In the agricultural context, the historic and current application of fertilizers and plant protectants, use of veterinary pharmaceuticals and hormones, strives to safeguard the growing food demands. In the context of a sprawling urban environment, waste, human pharmaceuticals, and urban pesticide outputs are increasing, with adequate runoff and sanitation infrastructure often lagging. Finally, industrial activities are associated with accidental leaks and spills, while the large-scale storage of industrial byproducts has led to legacy contaminants such as those stemming from raw mineral extraction. With this review paper, we aim to underscore the need for transdisciplinary research, along with transboundary communication, using sound science and adaptive policy and management practice in order to procure sustainable groundwater quality.

Chemical or Natural? Including LCA in Social CBA to Compare Remediation Alternatives for a Dry-Cleaning Facility

The choice between remediation alternatives for contaminated sites is complicated by different elements, e.g., the occurrence of multiple contaminants, the extent of the contamination, or the urban location, complicate the choice between remediation alternatives. This paper addresses this challenging choice by analyzing a case study of an extensive soil and groundwater contamination by a dry-cleaning company. For remediating this site, two alternatives were proposed. The first remediation alternative combines several techniques with in-situ chemical oxidization being the most important one. Due to the potential negative impact of this alternative on local residents a second remediation alternative was drawn up, in which the focus lies on the use of stimulated biological degradation. A Life Cycle Assessment (LCA) was performed on both alternatives and showed that the second alternative had a lower environmental impact. The inclusion of monetized LCA results in the calculation of a social Cost-Benefit Analysis (CBA) provided a more extensive view of the secondary environmental costs and benefits of the remediation alternatives. The results of the social CBA allow to conclude that both alternatives are not socially desirable, the chemical alternative however is socially less disadvantageous than the more natural remediation alternative.

Microbe and plant assisted-remediation of organic xenobiotics and its enhancement by genetically modified organisms and recombinant technology: A review

Environmental problems such as the deterioration of groundwater quality, soil degradation and various threats to human, animal and ecosystem health are closely related to the presence of high concentrations of organic xenobiotics in the environment. Employing appropriate technologies to remediate contaminated soils is crucial due to the site-specificity of most remediation methods. The limitations of conventional remediation technologies include poor environmental compatibility, high cost of implementation and poor public acceptability. This raises the call to employ biological methods for remediation. Bioremediation and microbe-assisted bioremediation (phytoremediation) offer many ecological and cost-associated benefits. The overall efficiency and performance of bio- and phytoremediation approaches can be enhanced by genetically modified microbes and plants. Moreover, phytoremediation can also be stimulated by suitable plant-microbe partnerships, i.e. plant-endophytic or plant-rhizospheric associations. Synergistic interactions between recombinant bacteria and genetically modified plants can further enhance the restoration of environments impacted by organic pollutants. Nevertheless, releasing genetically modified microbes and plants into the environment does pose potential risks. These can be minimized by adopting environmental biotechnological techniques and guidelines provided by environmental protection agencies and other regulatory frameworks. The current contribution provides a comprehensive overview on enhanced bioremediation and phytoremediation approaches using transgenic plants and microbes. It also sheds light on the mitigation of associated environmental risks.

Sorption mechanisms of chlorinated hydrocarbons on biochar produced from different feedstocks: Conclusions from single- and bi-solute experiments

Biochar is increasingly deemed a potential sorbent for contaminants in soil and water remediation. We tested three biochars from different feedstocks (cattle manure, grain husk, and wood chips) produced at relatively low pyrolysis temperature (450 °C), for their sorption behavior towards trichloroethylene (TCE) and tetrachloroethylene (PCE) in single- and bi-solute systems. In single-solute experiments, all biochars show stronger sorption for TCE (about 50% based on solubility-normalized Freundlich coefficients). The lower sorption of PCE is attributed to steric effects, e.g. size exclusion in small micropores and specific interactions. Plant-derived, carbon-rich biochars with high specific surface area and microporosity predominantly sorb via pore-filling, as also observed in activated carbon. Biochar produced from manure, with higher ash content and polarity, and smaller total pore volume (PV_tot), shows significant contribution of partitioning. These findings also apply to bi-solute systems. TCE and PCE show different competition behavior depending on biochar properties. Plant-based biochars are pore-filling-dominated and show strong competition. However, competition behavior in microporous biochars depends on the concentration range. Manure biochar with high polarity and low PV_tot shows significant partitioning and therefore less competition. Compared to the plant-based chars competition in manure biochar is not concentration-dependent. These results indicate that biochars with a large fraction of non-carbonized phase facilitate non-competitive sorption and might be a valuable sorbent in mixed contaminant systems.

Environmental contaminants and preeclampsia: a systematic literature review

Preeclampsia is a medical condition specific to pregnancy characterized by high blood pressure and protein in the woman's urine, indicating kidney damage. It is one of the most serious reproductive conditions, posing substantial risks to the baby and potentially fatal for the mother. The causes of preeclampsia are largely unknown and environmental contaminants merit further investigation. The aim of this review was to determine the association between environmental chemical exposures and preeclampsia. PubMed was searched for articles examining a priori chemical exposures and preeclampsia through April 2018. Studies were included in our review if they included at least 10 cases, evaluated preeclampsia independent of gestational hypertension, and used either measured or modeled exposure assessments. Our review contained 28 investigations examining persistent organic pollutants (POP) (6 studies), drinking water contaminants (1 study), atmospheric pollutants (11 studies), metals and metalloids (6 studies), and other environmental contaminants (4 studies). There were an insufficient number of investigations on most chemicals to draw definitive conclusions, but strong evidence existed for an association between preeclampsia and cadmium (Cd). There is suggestive evidence for associations between nitrogen dioxide (NO₂), particulate matter (PM)_2.5, and traffic exposure with preeclampsia. There is evidence for an association between preeclampsia and Cd but insufficient literature to evaluate many other environmental chemicals. Additional studies using repeated measures, appropriate biological matrices, and mixtures methods are needed to expand this area of research and address the limitations of previous studies.