Pentachloroethane Research Articles

Solvent Engineering of a Dopant-Free Spiro-OMeTAD Hole-Transport Layer for Centimeter-Scale Perovskite Solar Cells with High Efficiency and Thermal Stability.

High efficiency and environmental stability are mandatory performance requirements for commercialization of perovskite solar cells (PSCs). Herein, efficient centimeter-scale PSCs with improved stability were achieved by incorporating an additive-free 2,2',7,7'-tetrakis[N,N-di(p-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD) hole-transporting material (HTM) through simply substituting the usual chlorobenzene solvent with pentachloroethane (PC). A stabilized power conversion efficiency (PCE) of 16.1% under simulated AM 1.5G 1 sun illumination with an aperture of 1.00 cm2 was achieved for PSCs using an additive-free spiro-OMeTAD layer cast from PC. X-ray analysis suggested that chlorine radicals from PC transfer partially to spiro-OMeTAD and areretained in the HTM layer, resulting in conductivity improvement. Moreover, unencapsulated PSCs with a centimeter-scale active area cast from PC retained >70% of their initial PCE after ageing at 80 °C for 500 h, in contrast with less than 20% retention for control devices. Morphological and X-ray analyses of the aged cells revealed that the perovskite and HTM layers remain almost unchanged in the cells with a spiro-OMeTAD layer cast from PC whereas serious degradation occurred in the control cells. This study not only reveals the decomposition mechanism of PSCs in the presence of HTM additives but also opens up a broad range of organic semiconductors for radical doping.

Photocatalytic degradation of gaseous trichloroethylene on porous titanium dioxide pellets modified with copper(II) under visible light irradiation

Porous titanium dioxide pellets modified with copper(II) ion (Cu-TiO2) were synthesized by sol-gel method with dialysis for photocatalytic degradation of gaseous trichloroethylene (TCE) under visible light (VL) irradiation. TCE was completely degraded by passing the gas stream (mole fractions of oxygen and TCE were 0.2 and 1.75 × 10−4, respectively) at the flow rate of 25 mL min−1 through 0.2 g of the Cu-TiO2 pellets (Cu content: 0.1 atom%) calcined at 200 °C. TCE was converted mainly to carbon dioxide, dichloroacetic acid (DCAA), and inorganic chlorine species. Relatively small quantities of pentachloroethane (PCA) and trichloroacetaldehyde (TCAH) were detected as products on the Cu-TiO2 surface. Comparison with porous TiO2 pellets under ultraviolet irradiation revealed that more chlorinated products and less carbon dioxide were formed on Cu-TiO2 under VL irradiation. The mineralization of TCE to carbon dioxide was calculated to be only ca. 30.0%. It is noted that DCAA, PCA and TCAH were accumulated on the surface and were extracted with ethyl acetate. The porous Cu-TiO2 pellets show promise as the photocatalyst acting under VL irradiation for converting TCE gas to chlorinated compounds which can be used in industries.

A novel process integrating vacuum distillation with atmospheric chlorination reaction for flexible production of tetrachloroethane and pentachloroethane

Abstract In this paper, we developed a novel process integrating vacuum distillation with atmospheric chlorination reaction (VD-ACR) to realize the flexible production of tetrachloroethane (TeCA) and pentachloroethane (PCA) from 1,2-dichloroethane (DCA). During the simulation, the distillation column and reactors were operated for separation and chlorination respectively under variable pressures and temperatures. It is interesting to note that VD-ACR processes producing pure TeCA or PCA can exhibit the similar configuration parameters after optimization, which enables the flexible production of TeCA and PCA with different molar ratios via changing operating parameters. The molar ratio of TeCA/PCA can be fine-tuned within the range of 0.9:0.1 - 0.1:0.9 through adjusting the amount of chlorine pumped into side reactors, giving rise to the increase of the heat duty of reboiler by five times. A pilot-scale experiment was then operated based-upon this VD-ACR process and the result matched well with the simulation. Therefore, the VD-ACR model presented in this study will be beneficial for the industrial-scale flexible production of TeCA and PCA from DCA.

Ion mobility studies on the negative ion-molecule chemistry of pentachloroethane

In this study we present an investigation of the negative ion-molecule chemistry of pentachloroethane (PCE) in air based ion mobility spectrometry and ion mobility spectrometry–mass spectrometry systems. The observed product ions are Cl−, produced by dissociative electron attachment, and Cl−·HOO resulting from a reaction with O2−. Based upon the moisture content of the system, these ions can be observed as a doublet in a ‘dry’ system or as a singlet in a ‘wet’ system. The nature of the Cl−·HOO product ion was investigated by using isoflurane (ISOF) as a probe to monitor the changing ratios of Cl− and Cl−·HOO as the PCE concentration decreased. This confirmed the origins of the two product anions. Electronic structure calculations are provided. These have aided the understanding of the reaction processes observed.

Carbon and Chlorine Isotope Effects During Abiotic Reductive Dechlorination of Polychlorinated Ethanes

We investigated the extent and variability of C and Cl isotope fractionation during the reduction of polychlorinated ethanes to evaluate the potential use of Cl isotope analysis for the assessment of contaminant transformation in subsurface environments. Kinetic isotope effects (KIE) for C and Cl for the reductive beta-elimination of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), pentachloroethane (PCA), and hexachloroethane by Cr(II) used as model reductant in homogeneous solution were compared to KIEs measured for dehydrochlorination of 1,1,2,2-TeCA and PCA. Since isotopic reactions of polychlorinated compounds are complicated by the simultaneous presence of several Cl isotopologues and intramolecular isotopic competition, we present a procedure for the determination of KIEs for Cl from the initial reactant and final product Cl isotope ratios. Despite different reaction mechanisms, that is reduction via dissociative inner-sphere electron transfer by Cr(H2O)6(2+) and base-catalyzed, concerted elimination, respectively, apparent KIEs for C of both pathways fall within a similar range (1.021-1.031). In contrast, KIEs for Cl are significantly higher for reductive beta-elimination (1.013-1.021) than for dehydrochlorination (1.000-1.006). These results suggest that reductive transformations of polychlorinated contaminants might be identified on the basis of combined C and Cl isotope analysis.

Reduction of Chlorinated Ethanes by Nanosized Zero-Valent Iron: Kinetics, Pathways, and Effects of Reaction Conditions

Nanosized iron (< 100 nm in diameter) was synthesized in the laboratory and applied to the reduction of eight chlorinated ethanes (hexachloroethane (HCA), pentachloroethane (PCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,1,1-trichloroethane (1,1,1-TCA), 1,2-dichloroethane (1,2-DCA), and 1,1-dichloroethane (1,1-DCA)) in batch reactors. Reduction of 1,1,1-TCA increased linearly with increasing iron loading between 0.01 and 0.05 g per 124 mL solution (0.08-0.4 g/L). Varying initial concentrations of PCA between 0.025 and 0.125 mM resulted in relatively constant pseudo-first-order rate constants, indicating PCA removal conforms to pseudo-first-order kinetics. The reduction of 1,1,2,2-TeCA decreased with increasing pH; however, dehydrohalogenation of 1,1,2,2-TeCA became important at high pH. All chlorinated ethanes except 1,2-DCA were transformed to less chlorinated ethanes or ethenes. The surface-area-normalized rate constants from first-order kinetics analysis ranged from < 4 x 10(-6) to 0.80 L m(-2) h(-1). In general, the reactivity increased with increasing chlorination. Among tri- and tetrasubstituted compounds, the reactivity was higher for compounds with chlorine atoms more localized on a single carbon (e.g., 1,1,1-TCA > 1,1,2-TCA). Reductive beta-elimination was the major pathway for the chlorinated ethanes possessing alpha,beta-pairs of chlorine atoms to form chlorinated ethenes, which subsequently reacted with nanosized iron. Reductive alpha-elimination and hydrogenolysis were concurrent pathways for compounds possessing chlorine substitution on one carbon only, forming less chlorinated ethanes.

Hydrodechlorination of Chlorinated Ethanes by Nanoscale Pd/Fe Bimetallic Particles

Chlorinated ethanes are contaminants commonly found in soil and groundwater. The potential of nanoscale bimetallic (Fe∕Pd) particles for the hydrodechlorination of seven chlorinated ethanes (C2H6−xClx) was evaluated in batch experiments. Hexachloroethane (HCA) (C2Cl6), pentachloroethane (PCA) (C2HCl5), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA, C2H2Cl4), and 1,1,1,2-tetrachlorethane (1,1,1,2-TeCA, C2H2Cl4) were rapidly hydrodechlorinated (9–28 min half-lives) at a nanoparticle loading of 5 g/L. End products were ethane (61–87%) and ethylene (6–16%). Only one chlorinated intermediate, a corresponding β-elimination product, appeared temporarily during the reactions. Reductive dechlorination of 1,1,1-trichloroethane (1,1,1-TCA, C2H3Cl3) to ethane was completed at a relatively slower rate with half-life at 44.9 min. Little reduction of dichloroethane (C2H4Cl2) was observed within 24 h. The Pd/Fe bimetallic nanoparticles generally exhibit much higher reactivity when compared with conventional micro- and millimeter scale iron powders. The hydrodechlorination reactions are more complete, with a much higher yield of ethane and lower yield of chlorinated byproducts. A kinetic model incorporating a transition state species was proposed. Results from this work suggest that the Pd/Fe bimetallic nanoparticles may represent a treatment alternative for in situ remediation of chlorinated ethanes.

Total degradation of pentachloroethane by an engineered Alcaligenes strain expressing a modified camphor monooxygenase and a hybrid dioxygenase.

We engineered biphenyl-degrading Alcaligenes sp. strain KF711 for total degradation of pentachloroethane (PCA), which expresses a modified camphor monooxygenase and a hybrid dioxygenase consisting of TodC1 (a large subunit of toluene dioxygenase of Pseudomonas putida F1) and BphA2-BphA3-pbhA4 (a small subunit, ferredoxin and ferredoxin reductase of biphenyl dioxygenase, respectively, in strain KF707). Modified camphor monooxygenase genes (camCAB) were supplied as a plasmid and the todC1 gene was integrated within the chromosomal bph gene cluster by a single crossover recombination. The resultant strain KF711S-3cam dechlorinated PCA to trichloroethene by the action of the modified camphor monooxygenase under anaerobic conditions. The same strain subsequently degraded trichloroethene formed oxidatively by the action of the Tol-Bph hybrid dioxygenase under aerobic conditions. Thus sequential anaerobic and aerobic treatments of the KF711S-3cam resting cells resulted in efficient and total degradation of PCA.

Reduction of halogenated ethanes by green rust.

Green rusts, mixed Fe(II)/Fe(III) hydroxide minerals present in many suboxic environments, have been shown to reduce a number of organic and inorganic contaminants. The reduction of halogenated ethanes was examined in aqueous suspensions of green rust, both alone and with the addition of Ag(I) (AgGR) and Cu(II) (CuGR). Hexachloroethane (HCA), pentachloroethane (PCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,1-dichloroethane (1,1-DCA), and 1,2-dibromoethane were reduced in the presence of green rust alone, AgGR, or CuGR; only 1,2-dichloroethane and chloroethane were nonreactive. The reduction was generally more rapid for more highly substituted ethanes than for ethanes having fewer halogen groups (HCA > PCA > 1,1,1,2-TeCA > 1,1,1-TCA > 1,1,2,2-TeCA > 1,1,2-TCA > 1,1-DCA), and isomers with the more asymmetric distributions of halogen groups were more rapidly reduced than the isomer with greater symmetry (e.g., 1,1,1-TCA > 1,1,2-TCA). The addition of Ag(I) or Cu(II) to green rust suspensions resulted in a substantial increase in the rate of halogenated ethane reduction as well as significant differences in the product distributions with respect to green rust alone.

Dechlorination of pentachloroethane by commercial Fe and ferruginous smectite

Short-term experiments were conducted to investigate the effect of a commercial Fe and an iron-bearing clay mineral, ferruginuous smectite (SWa-1), on the degradation of pentachloroethane (PCA). After 3 h of contact time, SWa-1 catalyzed PCA dehydrochlorination to tetrachloroethene (PCE, 65% conversion), whereas commercial Fe promoted PCA stepwise dechlorination via dehydrochlorination (≈40% conversion) and subsequent PCE hydrogenolysis to trichloroethene (TCE). The addition of unaltered SWa-1 to commercial Fe led to a complete inhibition on TCE production, whereas the addition of reduced SWa-1 barely resulted in a 30% decrease.

Transformation of chlorinated aliphatic compounds by ferruginous smectite.

A series of chlorinated aliphatic compounds (RCI, including carbon tetrachloride (PCM), 1,1,1-trichloroethane (TCA), 1,1,2,2-tetrachloroethane (TeCA), pentachloroethane (PCA), hexachloroethane (HCA), trichloroethene (TCE), tetrachloroethene (PCE), trichloronitromethane (chloropicrin, CP), and trichloroacetonitrile (TCAN)) was reacted with ferruginuous smectite (sample SWa-1 from The Source Clays Repository), SWa, in aqueous suspension under anoxic conditions. Compounds highly polarizable or sharing substituents that facilitate charge delocalization adsorbed faster by reduced (SWa-R) than by unaltered (SWa-U) clay, indicating stronger dipole--dipole interactions between the substituents and the clay surface and/or hydrating water molecules. The reduction of the clay accelerated RCI adsorption up to 100-fold. Incubations with SWa-R promoted RCI reduction (CP, TCAN) or dehydrochlorination (TeCA and PCA). The reduction of structural Fe catalyzes the transformation of RCI via Brønsted and Lewis-basic promoted pathways. This study indicates that oxidation state of the structural Fe in SWa greatly alters surface chemistry and has a large impact on clay-organic interactions.

A physiologically based toxicokinetic model for lake trout ( Salvelinus namaycush)

A physiologically based toxicokinetic (PB-TK) model for fish, incorporating chemical exchange at the gill and accumulation in five tissue compartments, was parameterized and evaluated for lake trout ( Salvelinus namaycush). Individual-based model parameterization was used to examine the effect of natural variability in physiological, morphological, and physico-chemical parameters on model predictions. The PB-TK model was used to predict uptake of organic chemicals across the gill and accumulation in blood and tissues in lake trout. To evaluate the accuracy of the model, a total of 13 adult lake trout were exposed to waterborne 1,1,2,2-tetrachloroethane (TCE), pentachloroethane (PCE), and hexachloroethane (HCE), concurrently, for periods of 6, 12, 24 or 48 h. The measured and predicted concentrations of TCE, PCE and HCE in expired water, dorsal aortic blood and tissues were generally within a factor of two, and in most instances much closer. Variability noted in model predictions, based on the individual-based model parameterization used in this study, reproduced variability observed in measured concentrations. The inference is made that parameters influencing variability in measured blood and tissue concentrations of xenobiotics are included and accurately represented in the model. This model contributes to a better understanding of the fundamental processes that regulate the uptake and disposition of xenobiotic chemicals in the lake trout. This information is crucial to developing a better understanding of the dynamic relationships between contaminant exposure and hazard to the lake trout.

Kinetics of the Transformation of Halogenated Aliphatic Compounds by Iron Sulfide

The transformation of nine halogenated aliphatic compounds by 10 g/L (0.5 m2/L) FeS at pH 8.3 was studied in batch experiments. These compounds were as follows: pentachloroethane (PCA), 1,1,2,2- and 1,1,1,2-tetrachloroethanes (1122-TeCA and 1112-TeCA), 1,1,1- and 1,1,2-trichloroethanes (111-TCA and 112-TCA), 1,1- and 1,2-dichloroethanes (11-DCA and 12-DCA), carbon tetrachloride (CT), and tribromomethane (TBM). 11-DCA, 12-DCA, and 112-TCA showed no appreciable transformation by FeS over approximately 120 days, but the other compounds were transformed with half-lives of hours to days. PCA and 1122-TeCA underwent dehydrohalogenation faster than FeS-mediated reductive dehalogenation reactions under the conditions of these experiments. The remaining compounds for which significant transformation was observed underwent FeS-mediated reactions more rapidly than hydrolysis or dehydrohalogenation. For 1112-TeCA, the dihaloelimination product (1,1-dichloroethylene) was the only reaction product detected. For 111-TCA, CT, and TBM, hydrogenolysis products were the only products detected, although their mass recoveries were considerably less than 100%. Two simple log-linear correlations between rate constants and either one-electron reduction potentials or homolytic bond dissociation enthalpies were developed, with coefficients of determination (R 2 values) of 0.48 and 0.82, respectively. These findings are consistent with a rate-limiting step involving homolytic bond dissociation. However, neither correlation accurately described the reactivity of all the compounds that were studied, suggesting distinctions among the mechanisms for reductive dehalogenation of these compounds by FeS or the influence of additional molecular or thermodynamic parameters on rate constants.

Polychlorinated ethane reaction with zero-valent zinc: pathways and rate control

Efficient design of zero-valent metal permeable `barriers' for the reduction of organohalides requires information regarding the pertinent reaction rates as well as an understanding of the resultant distribution of products. In this study, the pathways and kinetics for reaction of polychlorinated ethanes with Zn(0) have been examined in batch reactors. Reductive β-elimination was the only route through which hexachloroethane (HCA), 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,1,2-trichloroethane (1,1,2-TCA) and 1,2-dichloroethane (1,2-DCA) reacted. Pentachloroethane (PCA) reacted via concurrent reductive β-elimination (93%) and hydrolysis (7%). As previously demonstrated, 1,1,1-trichloroethane (1,1,1-TCA) and 1,1-dichloroethane (1,1-DCA) reacted predominantly via reductive α-elimination. Attempts to correlate BET surface area-normalized rate constants ( k SA-BET) with one-electron reduction potential ( E 1) met with limited success, as HCA, PCA, 1,1,1,2-TeCA, and 1,1,1-TCA reacted at nearly identical rates despite substantial differences in E 1 values. Comparison of the pseudo-first-order rate constants ( k obs) for these species with rate constants ( k L a) obtained from a correlation for mass transfer to suspended particles revealed that the reaction of these species was mass transfer limited even though reaction rates were unaffected by mixing speed. Calculations suggest that mass transfer limitations may also play a role in the design of treatment systems for highly reactive species, with overall rate constants predicted to increase with flow velocity.

Respiratory–cardiovascular physiology and xenobiotic gill flux in the lake trout ( Salvelinus namaycush)

An in vivo respirometer–metabolism chamber was used to obtain respiratory–cardiovascular physiology under normoxic and hypoxic conditions, and xenobiotic gill absorption (flux) data on adult lake trout ( Salvelinus namaycush) over a 48-h exposure period at 11±1°C. An oral membrane was used to separate inspired and expired water flows, providing the first direct measurements of chemical flux across the gills of lake trout. Overall mean values (±S.D.) for normoxic respiratory function were: ventilation rate (V R)=53±9 # min −1, ventilation volume (Q V)=7±2 l kg −1 h −1, respiratory stroke volume (SV R)=2±1 ml, oxygen consumption (VO 2)=39±8 mg kg −1 h −1, oxygen utilization (U)=53±14%, and effective respiratory volume (Q W)=4±1 l kg −1 h −1. The resting Q V, Q W, and VO 2 seen in these lake trout were lower than seen previously in other salmonids. No significant differences ( P≥0.05) in respiratory function were detected between males and females. Trout subjected to hypoxia (30% of saturation) showed no changes in U or VO 2, while V R decreased (42±6 # min −1), Q V increased (22±6 l kg −1 h −1) and SV R increased (8±3 ml). Cardiovascular and blood gas measurements determined under normoxic conditions were heart rate (H R)=73±8 # min −1, cardiac output (Q C)=15±2 ml kg −1 min −1, cardiac stroke volume (SV H)=0.2 ml kg −1 min −1, dorsal aortic blood pressure (D BP)=34±1 mm Hg, ventral aortic blood pressure (V BP)=45±1 mm Hg, and venous oxygen partial pressure (P VO 2)=26±2 mm Hg. Initial 1-h mean±S.D. chemical gill extraction efficiencies (EE) for tetrachloroethane (TCE), pentachloroethane (PCE), and hexachloroethane (HCE) were 42±8, 58±16, and 68±17%, respectively. Forty-eight hour EE of 9±1% for TCE (log K OW=2.39) and 21±4% for PCE (log K OW=3.06) indicated they were approaching steady-state, in contrast to 54±13% for HCE (log K OW=4.04) which was not near steady-state. The EE for all three chloroethanes were significantly ( P<0.05) different from each other from 24 h to 48 h. Forty-eight hour lake trout mean cumulative chemical clearance (Cl X) values for waterborne TCE, PCE, and HCE were 64±11, 120±14, and 226±29 l kg −1, respectively. Lake trout Cl X and Q W for TCE, PCE, and HCE demonstrated an approximate 1:1 relationship indicative of water-flow limited gill absorption. Chemical gill absorption observed for the lake trout and chloroethanes was similar to the rainbow trout ( Oncorhynchus mykiss) from previous investigations and provided further support for the water-flow limited model of chemical flux across fish gills for mid-hydrophobic chemicals (log K OW=3.0–6.0).

Effects of Solution Composition and pH on the Reductive Dechlorination of Hexachloroethane by Iron Sulfide

Transition metal sulfide minerals are under investigation as potentially important abiotic reductants for chlorinated organic pollutants in anaerobic environments. This paper describes parametric rate studies done to evaluate the influence of environmental variables such as pH and ionic and organic solution composition on the reductive dechlorination of hexachloroethane (HCA) by FeS (poorly crystalline mackinawite). Results indicate that the reaction takes place at the mineral surface and is strongly pH-dependent. The influence of pH was explained by an acid/base equilibrium between two FeS surface species with different reactivities. Tetrachloroethylene was the principal reaction product, with pentachloroethane (PCA) as a minor intermediate and trichloroethylene, cis-1,2-dichloroethylene, and acetylene as minor products. Detection of PCA and the insensitivity of the reaction to numerous inorganic and organic solution species is consistent with an outersphere HCA dechlorination pathway involving two successive one-electron transfers. 2,2′-Bipyridine and 1,10-phenanthrolene significantly increased the rate of HCA dechlorination by FeS, which was explained by the participation of delocalized ﷿* molecular orbitals in the electron-transfer reaction. Cysteine and methionine were found to slow, but not stop, the reaction rate, and this was attributed to adsorption of thiol and sulfide functional groups to FeS surface iron atoms, causing an energetic or steric barrier to electron transfer. Rapid dechlorination rates and the insensitivity of the dechlorination reaction to numerous ionic and organic species suggest that FeS-mediated reductive dechlorination may be an important transformation pathway in natural systems.

Dermal Absorption of Three Waterborne Chloroethanes in Rainbow Trout (Oncorhynchus mykiss) and Channel Catfish (Ictalurus punctatus)

In vivoestimates of xenobiotic chemical flux across the dermal surface of intact fish were obtained by measuring chemical loss from venous blood to expired water. An experimental system was developed to separate the dermal route of exposure from all other routes. The system was then used to measure dermal absorption of tetrachloroethane (TCE), pentachloroethane (PCE), and hexachloroethane (HCE) in channel catfish (Ictalurus punctatus) and rainbow trout (Oncorhynchus mykiss), two fish with very different skin anatomies. The kinetics of accumulation varied among chemicals, but for each compound were similar among species. TCE accumulated rapidly, reaching steady state in blood within 48 hr. Steady state was not reached in 48 hr with PCE or HCE, although blood levels of PCE were probably close to steady-state values. Dermal flux estimates (based on branchial efflux) for TCE, PCE, and HCE were two to four times greater in catfish than in trout. Arterial blood concentrations of each compound were three to six times greater in catfish. These observations are indicative of greater flux across catfish skin, augmented by higher blood:water chemical partitioning. Trout skin is covered with scales and has no taste buds, while catfish skin does not possess scales and has numerous taste bud papillae. Both scales and taste bud papillae originate in the dermis and extend to the skin surface through the epidermis. In catfish these taste buds may offer channels through which chemicals diffuse across the epidermis to the more vascularized dermis. A comparison of dermal and branchial uptake was made by estimating zero-time dermal and branchial fluxes for all three chloroethanes. The mean dermal fluxes for TCE, PCE, and HCE ranged from 1.4 to 2.8, 1.8 to 3.6, and 1.4 to 3.2% of the total flux (branchial plus dermal) in rainbow trout and channel catfish, respectively. This research demonstrates that dermal absorption of waterborne chemicals occurs in large adult fish and results in distribution kinetics similar to those observed in inhalation exposures. Compared to branchial uptake, the dermal route of exposure appears to be relatively unimportant in large fish. It may, however, be very important in smaller fish and for juveniles of larger species.

A Physiologically Based Toxicokinetic Model for Dermal Absorption of Organic Chemicals by Fish

A physiologically based toxicokinetic model was developed to describe dermal absorption of waterborne organic chemicals by fish. The skin was modeled as a discrete compartment into which compounds diffuse as a function of chemical permeability and the concentration gradient. The model includes a countercurrent description of chemical flux at fish gills and was used to simulate dermal-only exposures, during which the gills act as a route of elimination. The model was evaluated by exposing adult rainbow trout and channel catfish to hexachloroethane (HCE), pentachloroethane (PCE), and 1,1,2,2-tetrachloroethane (TCE). Skin permeability coefficients were obtained by fitting model simulations to measured arterial blood data. Permeability coefficients increased with the number of chlorine substituent groups, but not in the manner expected from a directly proportional relationship between dermal permeability and skin:water chemical partitioning. An evaluation of rate limitations on dermal flux in both trout and catfish suggested that chemical absorption was limited more by diffusion across the skin than by blood flow to the skin. Modeling results from a hypothetical combined dermal and branchial exposure indicate that dermal uptake could contribute from 1.6% (TCE) to 3.5% (HCE) of initial uptake in trout. Dermal uptake rates in catfish are even higher than those in trout and could contribute from 7.1% (TCE) to 8.3% (PCE) of initial uptake in a combined exposure.

Dermal Absorption of Three Waterborne Chloroethanes in Rainbow Trout (Oncorhynchus mykiss) and Channel Catfish (Ictalurus punctatus)

In vivo estimates of xenobiotic chemical flux across the dermal surface of intact fish were obtained by measuring chemical loss from venous blood to expired water. An experimental system was developed to separate the dermal route of exposure from all other routes. The system was then used to measure dermal absorption of tetrachloroethane (TCE), pentachloroethane (PCE), and hexachloroethane (HCE) in channel catfish (Ictalurus punctatus) and rainbow trout (Oncorhynchus mykiss), two fish with very different skin anatomies. The kinetics of accumulation varied among chemicals, but for each compound were similar among species. TCE accumulated rapidly, reaching steady state in blood within 48 hr. Steady state was not reached in 48 hr with PCE or HCE, although blood levels of PCE were probably close to steady-state values. Dermal flux estimates (based on branchial efflux) for TCE, PCE, and HCE were two to four times greater in catfish than in trout. Arterial blood concentrations of each compound were three to six times greater in catfish. These observations are indicative of greater flux across catfish skin, augmented by higher blood:water chemical partitioning. Trout skin is covered with scales and has no taste buds, while catfish skin does not possess scales and has numerous taste bud papillae. Both scales and taste bud papillae originate in the dermis and extend to the skin surface through the epidermis. In catfish these taste buds may offer channels through which chemicals diffuse across the epidermis to the more vascu-larized dermis. A comparison of dermal and branchial uptake was made by estimating zero-time dermal and branchial fluxes for all three chloroethanes. The mean dermal fluxes for TCE, PCE, and HCE ranged from 1.4 to 2.8, 1.8 to 3.6, and 1.4 to 3.2% of the total flux (branchial plus dermal) in rainbow trout and channel catfish, respectively. This research demonstrates that dermal absorption of waterborne chemicals occurs in large adult fish and results in distribution kinetics similar to those observed in inhalation exposures. Compared to branchial uptake, the dermal route of exposure appears to be relatively unimportant in large fish. It may, however, be very important in smaller fish and for juveniles Of larger Species.

Correlation between murine liver cytochrome p450 2b1 induction by halogenated hydrocarbons and toxicity

The aim of this investigation was to study the relationship between the induction of cytochrome P450 2B1 isozymes by thirteen halogenated hydrocarbons and their toxicity. Each chemical, 1,1,2,2‐tetrabromoethane (1,1,2,2‐TBE), 1,1,1,2‐tetrachloroethane (1,1,1,2‐TCE), 1,1,2,2,‐tetrachloroethane (1,1,2,2‐TCE), pentachloroethane (PCE), 1,2‐dibromoethane (1,2‐DBE), iodoethane (IE), 1, 1‐dichloroethane (1,1‐DCE), 1,2‐dichloroethane (1,2‐DCE), 1,1,1‐trichloroethane (1,1,1‐TCE), 1,1,2‐trichloroethane (1,1,2‐TCE), dichloromethane (DCM), 1,1‐dichloroethylene (1,1‐DCEE) and trans 1,2‐dichloroethylene (t 1,2‐DCE) was administered (i.p.) in a dose‐response fashion (from 50 to 6.25% of the respective LD50) for three consecutive days, to Swiss Albino CD1 mice and the dealkylation of pentoxyresorufin examined in hepatic microsomes as 2B1 probe. For each hydrocarbon, linear regression was performed for both the inductive and toxic slope related to 2Bl‐like activity in order to evaluate the IC100 [the dose, in mmol/kg, pro...