摘要:

AbstractA historic account is provided of the development of quantitative structure‒activity relationships (QSARs) for the toxicity of simple nonelectrolyte organic compounds. The aquatic toxicity of many such compounds has been shown to be consistent with a narcosis mechanism involving pseudo‒steady‒state partitioning into a lipoidlike biophase site of action. These data are well fitted to a linear QSAR model involving solely the logPparameter.The toxicity of such nonelectrolytes administered by inhalation yields a linear QSAR based on the oil/gas partition coefficient. In contrast, the toxicity of these substances produced by nonequilibrium routes of administration, such as rat oral LD50, yields a parabolic or bilinear relationship consistent with observations published by Cros in France in 1863. Electrophile toxicants capable of forming covalent adducts with biochemical target molecules are more toxic than predicted by the corresponding narcosis models. Proelectrophile toxicants, which require metabolic activation to electrophiles, are also more toxic than would be predicted by narcosis

ISSN:0730-7268    

DOI:10.1002/etc.5620080101

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe products stoichiometry and kinetics of the reduction of trichloronitromethane (chloropicrin), bromotrichloromethane, carbon tetrachloride, ethylene dibromide and 1,2‐dibromo‐3‐chloropropane by iron(II) deuteroporphyrinlX, rat liver P‐450PBand P‐450 cam were compared with the reactions of reduced liver microsomes and the whole‐cell modelPseudomonas putida(PpG‐786). The polyhalomethanes in all cases undergo quantitative reductive hydrogenolysis\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm RCX}_n \, + \,2\,{\rm PFe}^{11} \, + \,{\rm H}^ + \to {\rm RCX}_{n - 1} \, + \,2{\rm PFe}^{{\rm III}} \, + \,{\rm X}^ - $$\end{document}The vicinal halides are Quantitatively converted by all P‐450 components to the corresponding olefinsIn contrast to the steric retardation of the rates exhibited by P‐450 cam, the rate constants for the mammalian enzyme were the same as those obtained for the heme in homogeneous solution. Microsomal reactions followed the same general reactivity patterns but on a much compressed scale. The whole‐cell conversions are apparently controlled in part by permeation; thus the microbial dehalogenation processes proceed at much slower rates than the actual chemistry that occurs at the active site. The results establish that the reductase capacities of widely divergent P‐450 cytochromes are consistent with the chemistry and mechanisms established for hemes in homogeneous solutions. Both microorganisms and mammals have the capacity to dehaloge

ISSN:0730-7268    

DOI:10.1002/etc.5620080102

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe estimation of properties of environmental interest is discussed. A general method for estimation based on molecular topology is presented and examples given for several studies. The most widely used topological method is based on the molecular connectivity indexes, which represent molecular structure in numerical form. Other methods presented include shape indexes and an additivity model. The variety of examples discussed and references given indicates the vitality of the use of molecular topology.

ISSN:0730-7268    

DOI:10.1002/etc.5620080103

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractSubstituted azobenzenes bind to the aryl hydrocarbon receptor protein about one to two orders of magnitude less strongly than does 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) when they carry substituents at some of the positions 2, 3, and 4 of the benzene rings. Positions 5 and 6 are disfavored. The results are interpreted in terms of the stability of azobenzene conformers and the extent to which the azobenzenes under study are isosteric with

ISSN:0730-7268    

DOI:10.1002/etc.5620080104

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractPhotooxidation of organic compounds takes place by direct and indirect photoprocesses. Generally, direct photooxidation rate constants cannot be predicted by currently available structure‐activity relationships (SARs). Indirect photooxidation processes, in which photogenerated oxidants react with chemicals by electron or H‐atom transfer or addition to unsaturated centers, are well understood and rate constants are strongly correlated with structure. This article reviews SARs for predicting rate constants for reactions of HO radical and ozone in the troposphere, and ROnradicals and singlet oxygen in water for reactive organic compounds, and discusses the identification, measurement and reactivity of these oxida

ISSN:0730-7268    

DOI:10.1002/etc.5620080105

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractStructure‐activity relationships were examined in toxicological studies with DDT‐type insecticides. The Taft σ* parameter for the electronegative character of substituents correlated well with the uptake of the analogs through insect tarsi and with acute oral toxicities to mice. Substituent groups with stronger electron‐withdrawing capacities penetrated more slowly through the insect cuticle and were markedly more toxic to mice. A nuclear magnetic resonance method was utilized to obtain estimated σ* values for use in the corre

ISSN:0730-7268    

DOI:10.1002/etc.5620080106

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractStructure‐activity analysis was used to evaluate the effects of 19 hazardous organic chemicals on microbial respiration in two slightly acidic soils (a Captina silt loam from Roane County Tennessee, and a McLaurin sandy loam from Stone County, Mississippi), both low in organic car bon and typical of the southeastern United States. Single additions of individual chemicals were applied at 1,000 μg/g (dry weight) soil, which was moistened to 80% base saturation and incubated in the dark at 20°C. CO2efflux from the soils was monitored at 24‐h intervals over a 6‐d period The chemicals included in the study were the following: acrylonitrile, furan, methyl ethyl ketone tetrahydrofuran, benzene, toluene, 1,2‐dichloroethane,p‐xylene, chlorobenzene, chloroform nitrobenzene,trans‐1,4‐dichloro‐2‐butene,cis‐1,4‐dichloro‐2‐butene, 1,2‐dichlorobenzene, 1,2,3 trichloropropane, carbon tetrachloride, 1,2‐dibromoethane (ethylene dibromide), 1,2,4,5 tetrachlorobenzene and hexachlorobenzene.Seventeen of the chemicals caused temporary depressions in CO2efflux in at least one soil, bu treatments were not significantly different from controls by the sixth day for most of these com pounds, indicating the ability of the microbial community to recover from chemically induced toxicity at this concentration. Acrylonitrile, nitrobenzene, and the 1,4‐dichloro‐2‐butenes causec sustained depressions, whereas methyl ethyl ketone and benzene increased respiration.The octanol/water partition coefficient (KOW) and molecular connectivity (1x) gave good correlations with effects on soil respiration for a subset of benzene and the six alkyl‐ and chloro substituted derivatives (i.e., toluene,p‐xylene, chlorobenzene, 1,2‐dichlorobenzene, 1,2,4,5

ISSN:0730-7268    

DOI:10.1002/etc.5620080107

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe degradation kinetics for several toxic organic compounds (p‐cresol, phenol,p‐chlorophenol, acetone and methanol) exposed to natural aquatic microbial assemblages were examined over a wide range of concentrations. Compounds were added in radiolabeled form and incubated at 25°C for periods ranging from several hours to one day. The results revealed that degradation kinetics were multiphasic for each of the compounds during at least one sampling period, i.e., the kinetic parametersKtandVmaxincreased with increasing substrate concentration. The observed multiphasicity suggests the presence within the natural microbial assemblages of multiple uptake/degradative systems, each with distinguishable kinetic parameters and each dominating degradation at a different substrate concentration range. If the kinetic diversity is ignored and rates of degradation are calculated based on the assumption that kinetics follow simple hyperbolic (Michaelis‐Menten) relationships, then errors as large as 40,000‐fold can result. Thus, our results suggest that models for predicting the persistence of such compounds in natural waters should consider changes in kinetic constants with substrate conce

ISSN:0730-7268    

DOI:10.1002/etc.5620080108

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractStudies were conducted to examine the adaptation response of aquifer microbial communities to xenobiotic compounds and the influence of chemical preexposure in the laboratory and in situ on adaptation. Adaptation and biodegradation were assessed as mineralization and cellular incorporation of14C‐radiolabeled substrates. For some compounds, such as ethylene dibromide, aniline andm‐nitrophenol, biodegradation and adaptation rates were not influenced by chemical concentration over the range tested. Biodegradation rates increased with concentration forp‐chlorophenol, and a gradient of adaptation and biodegradation responses was observed forp‐nitrophenol up to a threshold concentration. Acclimation to laboratory conditions decreased but did not eliminate the adaptation period top‐nitrophenol. Laboratory adaptation studies and examination of uncontaminated and contaminated field samples from a single aquifer indicated that adaptation was accompanied by shifts in the metabolic fate of the substrate. The increased metabolism associated with adapted communities was predominantly the result of increased mineralization. Cellular incorporation represented a significantly smaller fraction of total metabolism in the adapted versus the unadapted communities. The results indicate that the adaptation response in aquifer solids is due to a complex set of interactions that are influenced by the physiology and growth of the degrading po

ISSN:0730-7268    

DOI:10.1002/etc.5620080109

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractRainbow trout (Salmo gairdneri) and lake whitefish (Coregonus clupeaformis) were exposed for 72 d to109Cd in pelletized commercial trout food or in the water in a continuous‐flow water exposure system. Blood, gill, gut, liver, kidney, muscle, skin, feces and gut contents were sampled from 40 fish in each group during the exposure phase and from 20 fish in each group during the subsequent 56‐d depuration period. Gill accumulated the highest cadmium concentrations. After 56 d of depuration, most of the cadmium in food‐exposed fish of both species was in the kidney, gut and liver, but water‐exposed fish retained most of the cadmium in gill and kidney. Whole‐body concentration factors (L/kg wet weight tissue) after 72 d of exposure for water‐exposed fish were 55 for rainbow trout and 42 for whitefish. Whole‐body bioconcentration factors after 72 d of exposure for food‐exposed fish were less than 1 (kg food/kg dry weight tissue). Both species accumulated significantly greater proportions of the cadmium dose from food than from water. The percentages of the cadmium dose accumulated after 72 d of water exposure were 0.15% for trout and 0.11% for whitefish, while for food exposure the values were 1.03% for trout and 1.01% for whitefish. A simple two‐compartment kinetic model was fitted to the data. Equilibrium cadmium bioconcentration factors for aqueous exposure were estimated to be 161 for rainbow trout and 51 for lake whitefish. Biological half‐times for depuration ran

ISSN:0730-7268    

DOI:10.1002/etc.5620080110

出版商:Wiley Periodicals, Inc.    

年代:1989

数据来源: WILEY