Enantioselective Toxicity Effects of 2,2',3,5',6-Pentachloro Biphenyl (PCB-95) on Developing Brains in Zebrafish Larvae.

2,2',3,5',6-Pentachlorobiphenyl (PCB-95) is an environmentally relevant, chiral PCB congener that has been shown to act as a developmental neurotoxicant (DNT), targeting the developing brain. However, understanding enantioselective toxic effects for PCB-95 is in its infancy. To investigate these toxic effects, zebrafish embryos were exposed to racemates and enantiomers of PCB-95. Brain areas and pathology were studied. Results indicated dose dependent reduction of brain sizes with increased brain cell death in racemic and Ra (-)-PCB-95 treated groups. To provide a mechanistic basis for the observed neurotoxicity, gene expressions of antioxidant proteins such as Cu/Zn-SOD, Mn-SOD, and GPx were analysed. Antioxidant genes were up regulated with the PCB-95 exposure and racemic PCB-95 showed higher toxicity. These results suggest that the exposure to PCB-95 contributed to developmental neurotoxicity in early developing zebrafish larvae and may confer risks associated with enantioselective enrichment of PCB-95 in the environment.

Waste-Derived Nanoparticles: Synthesis Approaches, Environmental Applications, and Sustainability Considerations.

For the past few decades, a plethora of nanoparticles have been produced through various methods and utilized to advance technologies for environmental applications, including water treatment, detection of persistent pollutants, and soil/water remediation, amongst many others. The field of materials science and engineering is increasingly interested in increasing the sustainability of the processes involved in the production of nanoparticles, which motivates the exploration of alternative inputs for nanoparticle production as well as the implementation of green synthesis techniques. Herein, we start by overviewing the general aspects of nanoparticle synthesis from industrial, electric/electronic, and plastic waste. We expand on critical aspects of waste identification as a viable input for the treatment and recovery of metal- and carbon-based nanoparticles. We follow-up by discussing different governing mechanisms involved in the production of nanoparticles, and point to potential inferences throughout the synthesis processes. Next, we provide some examples of waste-derived nanoparticles utilized in a proof-of-concept demonstration of technologies for applications in water quality and safety. We conclude by discussing current challenges from the toxicological and life-cycle perspectives that must be taken into consideration before scale-up manufacturing and implementation of waste-derived nanoparticles.

Competitive Adsorption of Polycyclic Aromatic Hydrocarbons to Carbon Nanotubes and the Impact on Bioavailability to Fathead Minnow (Pimephales promelas).

Recent studies investigating the influence of carbon nanotubes (CNTs) on the bioavailability of organic contaminants have mostly focused on single-solute systems; however, a more likely scenario in the natural environment is a multisolute system where chemical interactions at the surface of the CNT may alter the bioavailability of these chemicals. In the present study bisolute adsorption isotherms of pairs of chemically similar polycyclic aromatic hydrocarbons (PAHs) by multiwalled carbon nanotubes (MWCNTs) were established, in conjunction with quantifying the bioavailability of the 2 competing MWCNT-adsorbed PAHs to Pimephales promelas using bile analysis by high-performance liquid chromatography with fluorescence detection. The results showed that whereas adsorption and bioavailability of chemically similar PAHs (anthracene and phenanthrene, and fluoranthene and pyrene) were the same in a single-solute system, in bisolute systems, PAHs that could better align or flex with the MWCNT surface due to morphological characteristics would outcompete the more rigid or planar PAHs. The bioavailability of individual PAHs in bisolute solutions increased by as much as 50% compared with single-solute solutions. However, the relationship between adsorption (i.e., Kd ) and concentration of PAH in the fish bile was similar in single and bisolute systems. This finding indicates that competitive interactions at the surface of MWCNTs influence bioavailability by way of altering adsorption affinity in a moderately predictable manner. Environ Toxicol Chem 2020;39:1702-1711. © 2020 SETAC.

Embryonic Exposure to 2,2',3,5',6-pentachlorobiphenyl (PCB-95) Causes Developmental Malformations in Zebrafish.

2,2',3,5',6-Pentachlorobiphenyl (PCB-95) is an environmental neurotoxicant. There is accumulated evidence that some neurotoxic effects of PCB-95 are caused by increased spontaneous Ca2+ oscillations in neurons resulting from modifying ryanodine receptors (RyR) in calcium-releasing channels. However, there are large gaps in explaining brain and other developmental malformations on embryonic PCB-95 exposure. In the present study, we address those deficiencies by studying the toxic effects of PCB-95 using zebrafish as an ontogenetic model. To characterize these effects, zebrafish embryos with intact chorions were exposed to 4 different concentrations of PCB-95 (0.25, 0.5, 0.75, and 1 ppm) for 3 consecutive days. The controls were maintained in 0.5 × E2 medium or egg water and in 0.1% (v/v) dimethyl sulfoxide (DMSO)/0.5 × E2 medium or egg water. PCB-95-treated groups showed dose-dependent decreases in survival and hatching rates, with increased rates of developmental malformations when compared to controls. These include morphological malformations, brain cell necrosis, and smaller eye sizes at 5 d post fertilization. These data suggest potential mechanisms underlying the abnormal behavior observed in a visual stimulus assay. The present study provides insight into PCB-95-induced developmental toxicity and supports the use of the zebrafish model in understanding the effects of PCB-95 exposure. Environ Toxicol Chem 2019;39:162-170. © 2019 SETAC.

Comparison of two reference black carbons using a planar PCB as a model sorbate.

In studies assessing sorption of hydrophobic organic compounds (HOCs) in natural systems, the choice of an appropriate reference black carbon, which can represent environmental black carbon (BC), is essential. This study compared isotherms of two commonly available and distinct reference BCs (n-hexane soot (BCRM) and diesel particulate matter (SRM 2975)) and a natural sediment from a source with little black carbon (Lake Hartwell, SC) using 3,3',4-trichlorobiphenyl (IUPAC #35) as a model sorbate. There was greater sorptivity for PCB-35 by BCRM than by SRM 2975. The observed differences in sorption between the two reference black carbons for PCB-35 may be ascribed to the different chemical characteristics of the black carbons. Differences in pore volume distribution at <16A pore width are less likely to be responsible for the observed differences in sorption. The elemental analysis confirmed that BCRM was a pure n-hexane soot because only C, H and O were measured. In contrast, SRM 2975 also contained N and S and a higher O% than BCRM. Compared to the low BC sediment, the two reference BCs had greater pore volume distributions, surface areas, total pore volumes and sorption. The observed nF (i.e., Freundlich exponent) values for PCB indicated greater linearity of the isotherms for the natural sediment than for the reference black carbons. For designing studies of sorption of HOCs in natural systems, in particular, when PCBs are contaminants of concern, results of this study can aid selection of the appropriate reference BCs.

Polychlorinated biphenyl contamination trends in Lake Hartwell, South Carolina (USA): sediment recovery profiles spanning two decades.

To assess the ca. 20-year polychlorinated biphenyl (PCB) contamination trends in Lake Hartwell, SC, sediment cores from the Twelve Mile Creek arm were collected in July 2004 at two sites (G30 and G33) first sampled in the mid-1980s. Congener-specific PCB data as a function of depth from the sediment-water interface for the 2004 sediment samples were compared to data obtained from 1987 and 1998 samples taken from the same locations. Despite modest decreases in total PCB levels near the G30 sediment-water interface, historical increases in average degrees of chlorination may elevate the overall toxic risk at this site. Unlike G30, the more rapid recovery in the near-surface sediment of G33 suggests that the effectiveness of the U.S. EPA natural attenuation record of decision is site-specific and is unlikely to result in uniform surface sediment recovery throughout the most contaminated regions of Lake Hartwell.

Enantiomeric composition of chiral polychlorinated biphenyl atropisomers in dated sediment cores.

Enantiomer fractions (EFs) of seven chiral polychlorinated biphenyls (PCBs) were measured in dated sediment cores of Lake Hartwell (SC, USA) and Lake Ontario (USA) to detect, quantify, and gain insight regarding microbial reductive dechlorination of PCBs in lake sediments with high and low concentrations, respectively. Lake Hartwell sediments had high total PCBs (5-60 microg/g), with significantly nonracemic EFs that generally were consistent with those from previous laboratory microcosm reductive dechlorination experiments using sediments from these sites. Thus, stereoselective reductive dechlorination had occurred in situ, including at total PCB concentrations of less than the threshold of approximately 30 to 80 microg/g suggested as being necessary for reductive dechlorination. Enantiomer fractions of PCBs 91, 95, 132, and 136 in Lake Hartwell cores were significantly correlated both with concentrations of those individual congeners and with total PCB concentration for some sites. This result indicates that enantioselective microbial dechlorination activity increases with higher concentrations within sediments for these congeners. Enantiomer composition reversed with depth for PCBs 91, 132, and 176, suggesting that multiple microbial populations may be present within the same core that are enantioselectively dechlorinating PCBs. Such observations indicate that concentration and time are not the only factors affecting biotransformation, complicating prediction of enantioselectivity. Comparison of EFs with dates suggested biotransformation half-lives of approximately 30 years, which is on the same time scale as sequestration by burial. In contrast, Lake Ontario sediments (maximum total PCBs, 400 ng/g) had racemic or near-racemic amounts of most congeners throughout the core profile, which is consistent with achiral indicators suggesting no microbial biotransformation within Lake Ontario sediments. Thresholds for reductive dechlorination may exist, but they would be at concentrations of less than 30 to 80 microg/g.

Trophic transfer of microplastics in aquatic ecosystems: Identifying critical research needs.

To evaluate the process of trophic transfer of microplastics, it is important to consider various abiotic and biotic factors involved in their ingestion, egestion, bioaccumulation, and biomagnification. Toward this end, a review of the literature on microplastics has been conducted to identify factors influencing their uptake and absorption; their residence times in organisms and bioaccumulation; the physical effects of their aggregation in gastrointestinal tracts; and their potential to act as vectors for the transfer of other contaminants. Limited field evidence from higher trophic level organisms in a variety of habitats suggests that trophic transfer of microplastics may be a common phenomenon and occurs concurrently with direct ingestion. Critical research needs include standardizing methods of field characterization of microplastics, quantifying uptake and depuration rates in organisms at different trophic levels, quantifying the influence that microplastics have on the uptake and/or depuration of environmental contaminants among different trophic levels, and investigating the potential for biomagnification of microplastic-associated chemicals. More integrated approaches involving computational modeling are required to fully assess trophic transfer of microplastics. Integr Environ Assess Manag 2017;13:505-509. © 2017 SETAC.

Sorption of humic acids and alpha-endosulfan by clay minerals.

Sorption of alpha-endosulfan by kaolinite and montmorillonite alone and in the presence of sorbed and dissolved humic acid (HA) was investigated (pH 8 and 25 degrees C). Three types of HA, Elliot soil HA (EHA), Peat HA (PHA), and Summit Hill HA (SHHA), were used to represent typical humic substances found in soils. For sorption of HA by either mineral, Freundlich sorption coefficient (K(f)) values appeared to decrease in the order of EHA > PHA > SHHA, which followed increasing polarity (expressed as the O/C atomic ratio) and decreasing percent-carbon content. For both clays, sorption of alpha-endosulfan by the HA mineral complex was greater than for sorption by the clay alone. Sorption of alpha-endosulfan by the HA mineral complexes followed the same order as the K(f) of the HAs (EHA > PHA > SHHA). Based on the amount of HA adsorbed by each mineral, organic carbon partition coefficients (K(oc)) were determined for sorption of alpha-endosulfan by two of the HA mineral complexes. The value of K(oc) for alpha-endosulfan sorption was greater for kaolinite EHA than kaolinite SHHA. However, the opposite trend was found with the montmorillonite HA complexes. Montmorillonite appeared to sorb alpha-endosulfan and/or HA with higher affinity than kaolinite, which likely is due to its 2:1 layer structure and higher surface area. Sorption of endosulfan diol, a hydrolysis product, by the minerals was much less than the parent pesticide.

Assessing atmospheric concentration of polychlorinated biphenyls by evergreen Rhododendron maximum next to a contaminated stream.

Conifers are often used as an air passive sampler, but few studies have focused on the implication of broadleaf evergreens to monitor atmospheric semivolatile organic compounds such as polychlorinated biphenyls (PCBs). In the present study, the authors used Rhododendron maximum (rhododendron) growing next to a contaminated stream to assess atmospheric PCB concentrations. The present study area was located in a rural setting and approximately 2 km downstream of a former capacitor plant. Leaves from the same mature shrubs were collected in late fall 2010 and winter and spring 2011. Polychlorinated biphenyls were detected in the collected leaves, suggesting that rhododendron can be used as air passive samplers in rural areas where active sampling is impractical. Estimated ΣPCB (47 congeners) concentrations in the atmosphere decreased from fall 2010 to spring 2011 with concentration means at 3990 pg m(-3) , 2850 pg m(-3) , and 931 pg m(-3) in fall 2010, winter 2011, and spring 2011, respectively. These results indicate that the atmospheric concentrations at this location continue to be high despite termination of active discharge from the former industrial source. Leaves had a consistent pattern of high concentrations of tetra-CBs and penta-CBs similar to the congener distribution in polyethylene passive samplers deployed in the water column, suggesting that volatilized PCBs from the stream were the primary source of contaminants in rhododendron leaves. Environ Toxicol Chem 2016;35:2192-2198. © 2016 SETAC.

Reductive dechlorination of polychlorinated biphenyls in sediment from the Twelve Mile Creek arm of Lake Hartwell, South Carolina, USA.

Lake Hartwell is a U.S. Army Corps of Engineers reservoir system located on the state line between South Carolina and Georgia, USA. The lake was contaminated with an estimated 200 metric tons of polychlorinated biphenyls ([PCBs]; mainly Aroclor 1016 and 1254), and the entire Twelve Mile Creek watershed and the Seneca River arm of Lake Hartwell were placed on the National Priorities List. Monitored natural attenuation was chosen as a remedy for the contaminated sediment. The relatively warm temperature of Lake Hartwell and lack of significant cocontaminants along with the PCBs distinguish this site from others that have been studied for microbially mediated reductive dechlorination. Microcosm studies were conducted with sediment from two locations in the Twelve Mile Creek arm and confirmed the presence of indigenous microorganisms capable of reductively dechlorinating Aroclor 1254, which contains predominantly tetra-, penta-, and hexachlorobiphenyl. The average number of total chlorines per biphenyl decreased from 4.8 to 4.9 to 2.9 to 3.0, following 250 to 260 d of incubation. The maximum observed dechlorination rates were 0.29 to 0.87 microg-atoms Cl- per gram sediment dry weight per week. The onset of dechlorination activity correlated strongly with maximum methanogenesis, which occurred without a lag in samples from the site that showed signs of in situ fermentation activity. Dechlorination occurred primarily at the meta and para positions (58-63% removal), with no apparent decrease in ortho chlorines. This most closely resembles pattern M, characterized by preferential removal of unflanked and flanked meta chlorines. The microcosm results are consistent with sediment cores analyzed from the same locations, which indicate accumulation with depth of the same ortho- and para-substituted congeners. It therefore appears that the success of monitored natural attenuation for Lake Hartwell will hinge on covering the recalcitrant PCBs with a sufficient amount of uncontaminated sediment to isolate them from the food chain.

Assessing ongoing sources of dissolved-phase polychlorinated biphenyls in a contaminated stream.

Few studies assess the potential of ongoing sources of "fresh" polychlorinated biphenyls (PCBs) to aquatic systems when direct discharge to the environment has been eliminated. In the present study, the authors used single-layered, low-density polyethylene samplers (PEs) to measure total PCB concentrations, congener profiles, and enantiomeric fractions (EFs) in a contaminated stream and to provide multiple lines of evidence for assessing ongoing inputs of PCB. Concentrations were well above background levels that have been monitored for years. Concentrations significantly increased with distance, the farthest downstream PE concentrations being almost five times greater than those at 79 m downstream of a historical point source. The PCBs in the PEs at 79 m downstream of the contamination source were dominated by low K(OW) congeners, similar to those in the mixture of Aroclors 1016 and 1254 (4:1 v/v) historically released from the former capacitor manufacturer. The only two chiral congeners detected in the PEs downstream were PCBs 91 and 95. The EF values were nonracemic for PCB 91, while the values were either racemic or near racemic for PCB 95. Increased PCB concentrations with distance and a congener composition of predominantly low-weight congeners in the PEs at 79 m downstream of the plant site suggested an ongoing PCB source from the plant site. Chiral signatures suggested aerobic biotransformation of dissolved PCBs but did not shed any light on possible ongoing PCB inputs.

Transformation of chiral polychlorinated biphenyls (PCBs) in a stream food web.

The enantiomeric composition of chiral PCB congeners was determined in Twelvemile Creek (Clemson, SC) to examine potential mechanisms of biotransformation in a stream food web. We measured enantiomeric fractions (EFs) of six PCB atropisomers (PCBs 84, 91, 95, 136, 149, and 174) in surface sediment, fine benthic organic matter (FBOM), coarse particulate organic matter (CPOM), periphyton, Asian clam, mayflies, yellowfin shiner, and semipermeable membrane devices (SPMDs) using gas chromatography (GC-ECD). Nonracemic EFs of PCBs 91, 95, 136, and 149 were measured in almost all samples. Enantiomeric compositions of PCBs 84 and 174 were infrequently detected with racemic EFs measured in samples except for a nonracemic EF of PCB 84 in clams. Nonracemic EFs of PCBs 91, 136, and 149 in SPMDs may be due to desorption of nonracemic residues from FBOM. EFs for some atropisomers were significantly different among FBOM, CPOM, and periphyton, suggesting that their microbial communities have different biotransformation processes. Nonracemic EFs in clams and fish suggest both in vivo biotransformation and uptake of nonracemic residues from their food sources. Longitudinal variability in EFs was generally low among congeners observed in matrices.

Chiral polychlorinated biphenyl transport, metabolism, and distribution: a review.

Chirality can be exploited to gain insight into enantioselective fate processes that may otherwise remain undetected because only biological, but not physical and chemical transport and transformation processes in an achiral environment will change enantiomer compositions. This review provides an in-depth overview of the application of chirality to the study of chiral polychlorinated biphenyls (PCBs), an important group of legacy pollutants. Like other chiral compounds, individual PCB enantiomers may interact enantioselectively (or enantiospecifically) with chiral macromolecules, such as cytochrome P-450 enzymes or ryanodine receptors, leading to differences in their toxicological effects and the enantioselective formation of chiral biotransformation products. Species and congener-specific enantiomer enrichment has been demonstrated in environmental compartments, wildlife, and mammals, including humans, typically due to a complex combination of biotransformation processes and uptake via the diet by passive diffusion. Changes in the enantiomer composition of chiral PCBs in the environment have been used to understand complex aerobic and anaerobic microbial transformation pathways, to delineate and quantify PCB sources and transport in the environment, to gain insight into the biotransformation of PCBs in aquatic food webs, and to investigate the enantioselective disposition of PCBs and their methylsulfonyl PCBs metabolites in rodents. Overall, changes in chiral signatures are powerful, but currently underutilized tools for studies of environmental and biological processes of PCBs.

PCB congeners and dechlorination in sediments of Lake Hartwell, South Carolina, determined from cores collected in 1987 and 1998.

Four sediment cores were collected from Lake Hartwell, SC, in 1987 and 1998 and analyzed for polychlorinated biphenyl (PCB) congeners. Total PCBs ranged from -0 to 58 microg/ g. Positive matrix factorization (PMF) was applied to the data sets to determine PCB source profiles. Two factors were determined for each data set. One factor resembled the original estimated PCB mixture of 80% Aroclor 1016 and 20% Aroclor 1254 and the other factor was a dechlorinated version of the mixture. Evidence of a dechlorination plateau is apparent from the PMF loading solutions because the dechlorinated congener profiles do not change from 1987 to 1998, butthe contribution to the profile from the dechlorinated factor increases from 73% (1987) to 87% (1998). PMF source contributions and plots of PCB concentration versus congener for individual samples provide evidence of enhanced dechlorination at high concentrations. After source apportionment an anaerobic dechlorination model was applied to the dechlorinated source profiles to quantify possible dechlorination pathways. It was found that dechlorination process M, extended to target biphenyl rings with up to six chlorines, provided the best fit for an individual process, and M + Q provides the best fit for combined processes, although M + LP also provides a similarfit. Process LP targets the higher chlorinated congeners and appears to dechlorinate PCBs in the sediments initially.

Assessment of natural attenuation via in situ reductive dechlorination of polychlorinated biphenyls in sediments of the Twelve Mile Creek arm of Lake Hartwell, SC.

Polychlorinated biphenyl (PCB)-contaminated sediment cores taken from five locations in Lake Hartwell, SC, with an increasing distance from the point source were evaluated for the presence of in situ reductive dechlorination of PCBs on the basis of a comparative congener-specific analysis of PCB distribution profiles between historical (1987) and current (1998) sediments from the same sites. A layer of 1998 sediment that was equivalent to 1987 sediment was determined by direct comparison of total PCB depth profiles after correction for any sedimentation that occurred at each location since 1987. Natural capping of contaminated sediments with the continued deposition of new sediments was observed in all locations except the one farthest from the source area. The residual PCB congeners accumulated in the field samples did not vary from site to site. Certain PCB congeners (e.g., 236-24 + 34-34, 245-25, and 23-4 CB) decreased with time and with depth along with an increase in lower chlorinated PCB congeners in all sampling locations. A similarity in distribution profiles between dechlorinated PCBs in laboratory microcosms and in the field samples was observed. These results provide supporting evidence that in situ reductive dechlorination has occurred in the Twelve Mile Creek arm of Lake Hartwell. Several sediment layers, particularlythe sites with highest PCB concentration, showed similar PCB distribution profiles between 1987 and 1998. An additional change in chlorine distribution between 1987 and 1998 at most "equivalent" depths was not observed. The ortho- and para-substituted congeners that accumulated during dechlorination of Aroclor 1254 after nearly 1 yr of incubation in the laboratory were the prominent residual products in all field samples. At a few locations and depths, evidence for dechlorination at surprisingly low concentrations (1-5 ppm) was observed. These results confirm that in situ reductive dechlorination of PCBs is operating at a very slow rate and may have been at a plateau since 1987 for certain depths and certain locations.

Changes in enantiomeric fractions during microbial reductive dechlorination of PCB132, PCB149, and araclor 1254 in Lake Hartwell sediment microcosms.

The enantioselectivity of microbial reductive dechlorination of chiral PCBs in sediments from Lake Hartwell, SC, was determined by microcosm studies and enantiomer-specific GC analysis. Sediments from two locations in the vicinity of the highest levels of PCB contamination were used as inocula. Dechlorination activity was monitored by concentration decreases in the spiked chiral PCBs and formation of dechlorination products using both achiral and chiral chromatography. Live microcosms spiked with PCB132 (234-236) exhibited dechlorination of PCB132 to PCB91 (236-24) and PCB51 (24-26). Meta dechlorination was the dominant mechanism. Microcosms spiked with PCB149 (245-236) exhibited preferential para dechlorination of PCB149 to PCB95 (236-25), followed by meta dechlorination to PCB53 (25-26) and subsequently PCB19 (26-2). Dechlorination of chiral PCB132 and PCB149 was not enantioselective. In Aroclor 1254-spiked microcosms, reductive dechlorination of PCB149 also was nonenantioselective. These results suggest that dechlorinating enzymes responsible for the dehalogenation of the chiral PCB132 and PCB149 congeners bind the two enantiomers equally. Reductive dechlorination of PCB91 and PCB95, however, occurred in an enantioselective manner, indicating that the dechlorinating enzymes for these PCBs are enantiomer-specific. The chlorine substitution pattern on the biphenyl ring appears to influence whether reductive dechlorination of chiral PCB congeners is enantioselective. Enantioselective PCB dechlorination by the microbial population of Lake Hartwell sediments occurs for select chiral PCBs; thus, certain chiral PCBs might be useful as markers for in situ reductive dechlorination.