Metabolic and mutagenicity studies on DDT and 15 derivatives. Detection of 1,1-bis(p-chlorophenyl)-2,2-dichloroethane and 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethyl acetate (kelthane acetate) as mutagens in Salmonella typhimurium and of 1,1-bis(p-chlorophenyl) ethylene oxide, a likely metabolite, as an alkylating agent

Effects of Long-Term Intake of DDT on Rats

DDT is a pesticide used in malaria-control programmes throughout the world. Its potential carcinogenicity was studied in MRC Porton rats (Wistar-derived) which received dietary concentrations of 0, 125, 250 and 500 parts per million DDT (technical-grade) for life. The treatment had no adverse effects on body growth or survival rate. Various types of tumours were observed in animals in all groups: exposure to DDT resulted in statistically significant increased incidence of liver-cell tumours only in female treated rats; one such tumour was observed in control rats. No metastases of these tumours were found.

Lack of Carcinogenicity of DDT in Hamsters

Syrian golden hamsters were fed for their lifespan a diet containing 0, 125, 250 and 500 parts per million (ppm) of DDT. The incidence of tumour bearing animals was 13 % among control females and ranged between 11-20 % in treated females. In control males 8 % had tumours. The incidence of tumour bearing animals among treated males ranged between 17-28 %. The incidence of adrenal cortex tumours showed a dose-related increase among the DDT-treated males. A liver-cell tumour and 2 liver hemangioendotheliomas were observed in 3 males treated with 250 ppm DDT. No liver-cell tumours were observed in the controls. No significant difference in tumour incidence was observed in treated versus control Syrian golden hamsters.

Sources and transformation pathways for dichlorodiphenyltrichloroethane (DDT) and metabolites in soils from Northwest Fujian, China

Dicofol (2,2,2-trichloro-1,1-bis-(p-chlorophenyl)ethanol) found in the environment is not only a miticide originated from commercial use, but also a metabolite of dichlorodiphenyltrichloroethane (DDT), which is often overlooked. To verify the sources and transformation pathways of DDT and related metabolites in soils, we measured p,p'-(dicofol + DBP) (sum of p,p'-dicofol and 4,4'-dichlorobenzophenone), DDT and six metabolites in soils from Northwest Fujian, China. The ratios of 1,1,1-trichloro-2-(o-chlorophenyl)-2-(p-chlorophenyl)ethane (o,p'-DDT)/1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDT) and the mass balance demonstrated that p,p'-(dicofol + DBP) predominantly originated from p,p'-DDT transformation rather than from actual dicofol application. p,p'-(dicofol + DBP) accounted for 45.0% as the primary metabolites of DDT in this study, more than 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDE) and 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDD), which might lead to large overestimations of the fresh DDT input by using the traditional ratio of (∑₂DDD + ∑₂DDE)/∑₂DDT (with all o,p'- and p,p'- isomers included). In paddy fields where the conditions alternate between aerobic (dry period) and anaerobic (wet period), both p,p'-DDD and p,p'-DDE were likely to degrade to 1-chloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDMU), which further transformed to 2,2-bis(p-chlorophenyl)ethylene (p,p'-DDNU). Degradation of p,p'-DDMU to p,p'-DDNU mainly occurred in waterlogged paddy soils. However, p,p'-DDNU might not transform to other higher-order metabolites in aerobic surface soils. Overall, our study confirmed p,p'-(dicofol + DBP) as metabolites of p,p'-DDT, suggested DDE and DDD were parallel precursors of DDMU, and further verified the transformation pathways of DDT in surface soils.

The influence of extreme river discharge conditions on the quality of suspended particulate matter in Rivers Meuse and Rhine (The Netherlands)

As a consequence of climate change, increased precipitation in winter and longer periods of decreased precipitation in summer are expected to cause more frequent episodes of very high or very low river discharge in the Netherlands. To study the impact of such extreme river discharge conditions on water quality, toxicity profiles and pollutant profiles were determined of suspended particulate matter (SPM) collected from Rivers Meuse and Rhine. Archived (1993-2003) and fresh (2009-2011) SPM samples were selected from the Dutch annual monitoring program of the national water bodies (MWTL), representing episodes with river discharge conditions ranging from very low to regular to very high. SPM extracts were tested in a battery of in vitro bioassays for their potency to interact with the androgen receptor (AR), the estrogen receptor (ER), the arylhydrocarbon receptor (AhR), and the thyroid hormone transporter protein transthyretin (TTR). SPM extracts were further tested for their mutagenic potency (Ames assay) and their potency to inhibit bacterial respiration (Vibrio fischeri bioluminescence assay). Target-analyzed pollutant concentrations of the SPM samples and additional sample information were retrieved from a public database of MWTL results. In vitro toxicity profiles and pollutant profiles were analyzed in relation to discharge conditions and in relation to each other using correlation analysis and multivariate statistics. Compared to regular discharge conditions, composition of SPM during very high River Meuse and Rhine discharges shifted to more coarse, sandy, organic carbon (OC) poor particles. On the contrary, very low discharge led to a shift to more fine, OC rich material, probably dominated by algae. This shift was most evident in River Meuse, which is characterized by almost stagnant water conditions during episodes of drought. During such episodes, SPM extracts from River Meuse demonstrated increased potencies to inhibit bacterial respiration and to compete with thyroid hormone to bind to TTR, possibly due to the presence of fycotoxins. Meanwhile concentrations of polychlorobiphenyls (PCBs) in SPM were also increased. Very high River Meuse discharges on the other hand corresponded to increased androgenic and AhR agoniztic responses, which coincided with increased PAH levels and PAH-related in vivo risk estimates (i.e. multi-substance potentially affected fraction of species; msPAF). In River Rhine, very high discharges also corresponded to increasing androgenic potencies in SPM. Concentrations and corresponding msPAF values of PAHs (and metals), however, decreased with very high discharges in River Rhine in contrast to River Meuse. Mutagenicity was observed for SPM extracts from River Rhine collected during all discharge conditions, except during regular discharge. Aggregated toxicity index values, which were useful to identify toxicity profiles deviating from the generally observed pattern, did not correlate with river discharges, probably due to opposite effects of discharge conditions on different bioassay responses. In conclusion, SPM quality and related in vivo risk estimates changed during very low or very high discharge conditions but the changes were specific for the different toxic endpoints and pollutants in the different rivers. Moreover, bioassay responses to a series of consecutively collected samples from River Rhine during the Christmas flood of 1993 indicated that SPM quality is variable within a single episode of extreme discharge.

Toxicity, dioxin-like activities, and endocrine effects of DDT metabolites--DDA, DDMU, DDMS, and DDCN

BACKGROUND, AIM, AND SCOPE

2,2-bis(chlorophenyl)-1,1,1-trichloroethane (DDT) metabolites, other than those routinely measured [i.e., 2,2-bis(chlorophenyl)-1,1-dichloroethylene (DDE) and 2,2-bis(chlorophenyl)-1,1-dichloroethane (DDD)], have recently been detected in elevated concentrations not only in the surface water of Teltow Canal, Berlin, but also in sediment samples from Elbe tributaries (e.g., Mulde and Havel/Spree). This was paralleled by recent reports that multiple other metabolites could emerge from the degradation of parent DDT by naturally occurring organisms or by interaction with some heavy metals. Nevertheless, only very few data on the biological activities of these metabolites are available to date. The objective of this communication is to evaluate, for the first time, the cytotoxicity, dioxin-like activity, and estrogenicity of the least-studied DDT metabolites.

METHODS

Four DDT metabolites, p,p'-2,2-bis(chlorophenyl)-1-chloroethylene (DDMU), p,p'-2,2-bis(chlorophenyl)-1-chloroethane (DDMS), p,p'-2,2-bis(4-ch1oropheny1)acetonitrile (DDCN), and p,p'-2,2-bis(chlorophenyl)acetic acid (DDA), were selected based on their presence in environmental samples in Germany such as in sediments from the Mulde River and Teltow Canal. O,p'-DDT was used as reference in all assays. Cytotoxicity was measured by neutral red retention with the permanent cell line RTG-2 of rainbow trout (Oncorhynchus mykiss). Dioxin-like activity was determined using the 7-ethoxyresorufin-O-deetylase assay. The estrogenic potential was tested in a dot blot/RNAse protection-assay with primary hepatocytes from male rainbow trout (O. mykiss) and in a yeast estrogen screen (YES) assay.

RESULTS

All DDT metabolites tested revealed a clear dose-response relationship for cytotoxicity in RTG-2 cells, but no dioxin-like activities with RTL-W1 cells. The dot blot/RNAse protection-assay demonstrated that the highest non-toxic concentrations of these DDT metabolites (50 μM) had vitellogenin-induction potentials comparable to the positive control (1 nM 17β-estradiol). The estrogenic activities could be ranked as o,p'-DDT > p,p'-DDMS > p,p'-DDMU > p,p'-DDCN. In contrast, p,p'-DDA showed a moderate anti-estrogenic effect. In the YES assay, besides the reference o,p'-DDT, p,p'-DDMS and p,p'-DDMU displayed dose-dependent estrogenic potentials, whereas p,p'-DDCN and p,p'-DDA did not show any estrogenic potential.

DISCUSSION

The reference toxicant o,p'-DDT displayed a similar spectrum of estrogenic activities similar to 17β-estradiol, however, with a lower potency. Both p,p'-DDMS and p,p'-DDMU were also shown to have dose-dependent estrogenic potentials, which were much lower than the reference o,p'-DDT, in both the vitellogenin and YES bioassays. Interestingly, p,p'-DDA did not show estrogenic activity but rather displayed a tendency towards anti-estrogenic activity by inhibiting the estrogenic effect of 17β-estradiol. The results also showed that the p,p'-metabolites DDMU, DDMS, DDCN, and DDA do not show any dioxin-like activities in RTL-W1 cells, thus resembling the major DDT metabolites DDD and DDE.

CONCLUSIONS

All the DDT metabolites tested did not exhibit dioxin-like activities in RTL-W1 cells, but show cytotoxic and estrogenic activities. Based on the results of the in vitro assays used in our study and on the reported concentrations of DDT metabolites in contaminated sediments, such substances could, in the future, pose interference with the normal reproductive and endocrine functions in various organisms exposed to these chemicals. Consequently, there is an urgent need to examine more comprehensively the risk of environmental concentrations of the investigated DDT metabolites using in vivo studies. However, this should be paralleled also by periodic evaluation and monitoring of the current levels of the DDT metabolites in environmental matrices.

RECOMMENDATIONS AND PERSPECTIVES

Our results clearly point out the need to integrate the potential ecotoxicological risks associated with the "neglected" p,p'-DDT metabolites. For instance, these DDT metabolites should be integrated into sediment risk assessment initiatives in contaminated areas. One major challenge would be the identification of baseline data for such risk assessment. Further studies are also warranted to determine possible additive, synergistic, or antagonistic effects that may interfere with the fundamental cytotoxicity and endocrine activities of these metabolites. For a more conclusive assessment of the spectrum of DDT metabolites, additional bioassays are needed to identify potential anti-estrogenic, androgenic, and/or anti-androgenic effects.

Field validation of anaerobic degradation pathways for dichlorodiphenyltrichloroethane (DDT) and 13 metabolites in marine sediment cores from China

Although the production and use of dichlorodiphenyltrichloroethane (DDT), a legacy component of persistent organic pollutants, have been highly restricted worldwide, the environmental fate of DDT has remained a great concern as it is not only ubiquitous and bioaccumulative but can also be degraded to a series of metabolites that may be more hazardous ecologically. The present study, taking advantage of the abundant levels of DDT and its metabolites in a subtropical coastal region of China, investigated into the degradation pathways of DDT in natural coastal sediment. Sediment profiles indicated that degradation of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDT) to 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDD) mainly occurred in sediment of the top 20 cm layer. 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDE), aerobically transformed from p,p'-DDT prior to sedimentation, was likely to degrade to 1-chloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDMU) which was further converted to 2,2-bis(p-chlorophenyl)ethylene (p,p'-DDNU). In addition, p,p'-DDNU could be transformed to 2,2-bis(p-chlorophenyl)ethane (p,p'-DDNS) and other high-order metabolites. On the other hand, the conversions of p,p'-DDD to p,p'-DDMU and 1-chloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDMS) to p,p'-DDNU were deemed slow in anaerobic sediment. Therefore, the present study confirmed all the degradation pathways involving reductive dechlorination and p,p'-DDE being a more important precursor for p,p'-DDMU than p,p'-DDD in anaerobic sediment, as proposed previously. On the other hand, the present study suggested that p,p'-DDMU instead of p,p'-DDMS was more likely the precursor for formation of high-order metabolites. Based on the current assessments, use of (DDD+DDE)/DDTs to indicate whether there is fresh DDT input may lead to large uncertainties if the concentrations of high-order metabolites are not negligible. Similarly, ecological risk assessment associated with DDT should be conducted with consideration of high-order DDT metabolites.

Toxicological characteristics of endocrine-disrupting chemicals: developmental toxicity, carcinogenicity, and mutagenicity

It is generally accepted that endocrine-disrupting chemicals (EDCs) play a role in a variety of adverse health effects in an intact organism or its progeny as a consequence of changes in the endocrine system. Primary toxic effects of EDCs were reported to be related to infertility, reduction in sperm count, and teratogenicity, but other important toxic effects of EDCs such as carcinogenicity and mutagenicity have also been demonstrated. The aim of the present study was to systematically analyze the toxicological characteristics of EDCs in pesticides, industrial chemicals, and metals. A comprehensive literature survey on the 48 EDCs classified by the Centers for Disease Control and Prevention (CDC) was conducted using a number of databases which included Medline, Toxline, and Toxnet. The survey results revealed that toxicological characteristics of EDCs were shown to produce developmental toxicity (81%), carcinogenicity (79%, when positive in at least one animal species; 48%, when classified based on IARC evaluation), mutagenicity (79%), immunotoxicity (52%), and neurotoxicity (50%). Regarding the hormone-modulating effects of the 48 EDCs, estrogenic effects were the most predominant in pesticides, while effects on thyroid hormone were found for heavy metals. EDCs showing estrogen-modulating effects were closely related to carcinogenicity or mutagenicity with a high degree of sensitivity. Systematic information on the toxicological characteristics of the EDCs will be useful for future research directions on EDCs, the development of new screening methods, legal regulation, and for investigations of their mechanism of action.

Application of QSTRs in the selection of a surrogate toxicity value for a chemical of concern

As part of the EPA's mission to protect the environment, chemicals of concern (CoCs) at Superfund or other hazardous waste sites are cleaned up based on their potential toxicity to humans and the surrounding ecosystem. Oftentimes, there is a lack of experimental toxicity data to assess the health effects for a CoC in the literature. This research describes a method using Quantitative Structure Toxicity Relationships (QSTRs) for identifying a surrogate chemical for any given CoC. The toxicity data of the surrogate chemical can then be used to rank hazardous waste-site chemicals prior to cleanup decisions. A commercial QSTR model, TOPKAT, was used to establish structural and descriptor similarity between the CoC and the compounds in the QSTR model database using the Oral Rat Chronic LOAEL model. All database chemicals within a similarity distance of < or = 0.200 from the CoC are considered as potential surrogates. If the CoC fails to satisfy model considerations for the LOAEL model, no surrogate is suggested. Potential surrogates that have toxicity data on Integrated Risk Information System (IRIS), Health Effects Assessment Summary Tables (HEAST), or National Center for Environmental Assessment (NCEA) provisional toxicity value list become candidate surrogates. If more than one candidate surrogate is identified, the chemical with the most conservative RfD is suggested as the surrogate. The procedure was applied to determine an appropriate surrogate for dichlorobenzophenone (DCBP), a metabolite of chlorobenzilate, dichlorodiphenyltrichloroethane, and dicofol. Forty-seven potential surrogates were identified that were within the similarity distance of < or = 0.200, of which only five chemicals had an RfD on IRIS, HEAST, or on the NCEA provisional toxicity value list. Among the five potential surrogates, chlorobenzilate with an RfD of 2 x 10(-2) mg/kg-day was chosen as a surrogate for DCBP as it had the most conservative toxicity value. This compared well with surrogate selection using available metabolic information for DCBP and its metabolites or parent compounds in the literature and the provisional toxicity value of 3 x 10(-2) mg/kg-day that NCEA developed using a subchronic study.

The genetic toxicology of putative nongenotoxic carcinogens

This report examines a group of putative nongenotoxic carcinogens that have been cited in the published literature. Using short-term test data from the U.S. Environmental Protection Agency/International Agency for Research on Cancer genetic activity profile (EPA/IARC GAP) database we have classified these agents on the basis of their mutagenicity emphasizing three genetic endpoints: gene mutation, chromosomal aberration and aneuploidy. On the basis of results of short-term tests for these effects, we have defined criteria for evidence of mutagenicity (and nonmutagenicity) and have applied these criteria in classifying the group of putative nongenotoxic carcinogens. The results from this evaluation based on the EPA/IARC GAP database are presented along with a summary of the short-term test data for each chemical and the relevant carcinogenicity results from the NTP, Gene-Tox and IARC databases. The data clearly demonstrate that many of the putative nongenotoxic carcinogens that have been adequately tested in short-term bioassays induce gene or chromosomal mutations or aneuploidy.

Species differences in enzymes controlling reactive epoxides

Activities of enzymes involved in the metabolic formation and catabolism of epoxides were determined in liver subcellular preparations from 11 mammalian species and various strains of mice. The most conspicuous finding was that the activities of the microsomal epoxide hydrolase were clearly lower in the mouse than in the other species. This invited the working hypothesis that epoxides may be involved in mouse liver carcinogenesis. The carcinogens may be metabolised themselves to reactive epoxides or they may modify the metabolism of epoxides formed from endogenous or other foreign compounds. To examine the former point, phenobarbital, DDT (1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane), lindane and benzo(a)pyrene were investigated for mutagenicity in Salmonella typhimurium using as the carcinogen-metabolising system subcellular liver preparations from animals in which these compounds efficiently induce liver tumours and from resistant animals. Phenobarbital, DDT and lindane were not mutagenic under any conditions, including those where microsomal epoxide hydrolase was also inhibited. However, a DDT metabolite, 1,1-bis(p-chlorophenyl)-2,2-dichloroethane was mutagenic in strain TA98, when norharman was added to the metabolising system, rat liver postmitochondrial fraction. Benzo(a)pyrene, which efficiently induces liver tumours in male but not in female newborn C3HeB/FeJ X A/J mice, was similarly activated by liver preparations from male and female animals. This was true with and without pretreatment of the mice with an inducer of cytochrome P-448. Also, activities and inducibilities of monooxygenase, epoxide hydrolase and glutathione transferase (toward benzo(a)pyrene and benzo(a)pyrene 4,5-oxide, respectively) were indistinguishable between males and females. Therefore, differences in the metabolism of benzo(a)pyrene do not appear to be the reason for the sex difference in tumour susceptibility. Likewise, mouse strains with high and low frequencies of spontaneous and chemically-induced liver tumours did not appreciably differ in their hepatic microsomal epoxide hydrolase activities. The low level of this activity therefore cannot constitute the critical factor for the high tumour susceptibility of certain strains of mice. However the statement does not preclude potentiation of the susceptibility toward particular carcinogens owing to this metabolic trait of the mouse.

o,p'-DDD in the mouse lung: selective uptake, covalent binding and effect on drug metabolism

By means of autoradiography a high and selective accumulation was observed in the lung alveolar region of C57Bl mice injected with o,p'-[14C]DDD. Exhaustive extraction of lung tissue showed that a large fraction of the radioactivity was covalently bound to protein. Covalent binding in liver was 20-30 times lower and represented a smaller fraction of the total radioactivity present in this tissue. Formation of a cytochrome P-450 catalysed reactive metabolite in lung and liver was indicated by a decreased covalent binding in these tissues in mice pretreated with metyrapone. Both beta-naphthoflavone (beta NF) and phenobarbital (PB) pretreatment decreased binding of o,p'-DDD in lung tissue, while binding in the liver was induced by PB but remained unaffected by beta NF. Pretreatment with high doses of o,p'-DDD and p,p'-DDT gave a significantly decreased binding of o,p'-[14C]DDD in lung, whereas binding in liver remained unchanged. Conjugation with glutathione does not appear to be a major inactivation pathway for the reactive lung metabolite, since a high dose of o,p'-DDD did not deplete non-protein thiols (NPSH) in lung tissue. Pretreatment with o,p'-DDD decreased the N-demethylation of [dimethyl-14C]aminopyrine in both lung and liver in a dose-dependent manner, suggesting that the drug-metabolizing enzyme system may be a target for o,p'-DDD in vivo.

Metabolism-dependent binding of the chlorinated insecticide DDT and its metabolite, DDD, to microsomal protein and lipids

Dichlorodi[U-14C]phenyltrichloroethane ( [14C]DDT), incubated with rat hepatic microsomes and NADPH, produced reactive intermediates which covalently bound to microsomal protein and lipids. In atmospheric oxygen, DDT bound to microsomal protein; however, binding was increased up to approximately 70% by oxygen depletion. Low levels of [14C]DDT binding to microsomal lipids occurred under atmospheric oxygen but, in contrast to protein binding, DDT-phospholipid binding was increased up to 20-fold by oxygen depletion. Dichlorodiphenyldichloroethane (DDD) was rapidly formed from DDT under anaerobic conditions, although when DDD was utilized as substrate, binding to microsomal protein occurred only in the presence of oxygen. Sodium dithionite, added to microsomes, produced [14C]DDT phospholipid and protein binding, and DDD formation, but failed to support DDD metabolism or binding. The data are consistent with the reductive formation of a DDT free-radical intermediate that led to the formation of DDD and that was bound preferentially to microsomal lipids.

Implications of multiple mechanisms of carcinogenesis for short-term testing

The attempt has been made recently to categorize carcinogens into two mechanistic types based on their mechanism of action: genotoxic (capable of reacting with and damaging DNA) and epigenetic (unable to damage DNA to any detectable extent). By requiring that a given chemical fit into one or the other of these narrowly defined categories for regulatory purposes, we are probably oversimplifying potential biological effects. In fact, based on our limited understanding of carcinogenic mechanisms, this artificial distinction should probably be abandoned in favor of a more precise statement of each chemical's mechanism or relative potency of initiating and promoting effects. Since the standard short-term tests by which carcinogenicity of chemicals is screened were designed to detect certain chemical classes with active electrophilic intermediates, weak or specialized carcinogens may be missed and may be assumed erroneously to be nongenotoxic. The mechanisms of carcinogenicity for such carcinogens may include particulate deposition, active radical formation, liver toxicity, and hormonal interactions. Not all of these secondary mechanisms depend upon a detectable level of binding to DNA, damage to DNA, or modification of the DNA sequence, even though they may demonstrate other characteristics of a complete carcinogen (that is, irreversibility and lack of a threshold). Certain agents have been labeled as epigenetic. However, a consideration of the literature on sample agents (diethylstilbestrol, asbestos, and urethane) reveals that these are not epigenetic carcinogens despite their being labeled as such. Agents with irreversibility and no threshold have initiating potential and, as such, are genotoxic, whereas carcinogens that are classified as nongenotoxic are largely agents that promote the growth of liver tumors. Even promotion can be a mechanistically specialized phenomenon. For example, some promoters are cytotoxic to the liver, but not all liver toxins are liver tumor promoters or liver carcinogens. Further, the carcinogens commonly labeled as epigenetic might cause a unique specialized genotoxicity not detected by common screening tests routinely used for detecting genotoxicity. If we assume that this unrecognized but necessary initiating potential is mediated by some specialized genotoxicity, extra care must be taken to establish a genuine lack of genotoxicity before an agent can be classified (and regulated) as a promoter (lacking the ability to initiate tumor growth but still enhancing tumor development).(ABSTRACT TRUNCATED AT 400 WORDS)

[The enzymatic degradation of DDT. 1. Main degradation pathways]

First investigations on the degradation of DDT were already carried out at the beginning of its application. Its metabolism, however, is not yet absolutely clear till now. Main degradation pathways are considered: Reductive dechlorinations, successive dehydrochlorinations to unsaturated compounds as well as oxidations to aldehydes, alcohol and carboxylic acid. Decarboxylations of carboxylic acids are considered to be dependent on the species concerned. Between various organisms only quantitative differences are evident.

Metabolism of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane in the mouse

The metabolites of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) found in the urine of female Swiss mice are reported. The metabolites of DDT are DDD, 1-chloro-2,2-bis(p-chlorophenyl)ethene (DDMU), 1,1-dichloro-2-bis(p-chlorophenyl)ethene (DDE), 2,2-bis(p-chlorophenyl)acetic acid (DDA), 2-hydroxy-2,2-bis(p-chlorophenyl)acetic acid (alpha OH-DDA) and 2,2-bis(p-chlorophenyl)ethanol (DDOH), while DDD afforded DDMU, DDE, DDA, alpha OH-DDA and DDOH. The relative excreted levels of DDA and DDOH and the absence of 2,2-bis(p-chlorophenyl)acetaldehyde (DDCHO) are not consistent with the generally accepted pathway for DDA formation, which involves sequential metabolism of DDT and DDD via DDOH to afford DDA. The quantitative results are interpreted to mean that DDA is formed by hydroxylation at the chlorinated sp3-side chain carbon of DDD to give 2,2-bis(p-chlorophenyl)acetyl chloride (DDA-Cl), which in turn is hydrolyzed to DDA. The excretion of alpha OH-DDA from both DDT- and DDD-treated mice has never been previously observed. It is suggested that this metabolite arises from the initial epoxidation of DDMU, a metabolite of DDT and DDD, to yield 1,2-epoxy-1-chloro-2,2-bis(p-chlorophenyl)ethane (DDMU-epoxide). This chloroepoxide is then hydrolyzed and oxidized to produce the alpha OH-DDA.

Correlation of alkylating and mutagenic activities of allyl and allylic compounds: standard alkylation test vs. kinetic investigation

Thirty-nine allylic and non-allylic compounds have been tested in the standard 4-(p-nitrobenzyl)pyridine (NBP) alkylating procedure and the Salmonella typhimurium mutagenicity assay. Fourteen of these were found directly mutagenic (without addition of S-9 mix activating enzyme system). With twelve of these compounds, a good correlation of alkylating and mutagenic potencies was established; the remaining two do not meet the chemical conditions of the NBP procedure on account of HCl elimination with these two compounds. The other 25 substances were inactive in both systems. The quantitative correlation proved to be almost linear in the lower activity ranges (E approximately 2; revertants/muml approximately 600). The reasons for some deviations from the linear relationship have been analyzed and discussed on the basis of structural features. In addition to the standard alkylation test, a modified NBP-test was performed in order to obtain kinetic data and activation energy values. The results with 6 representative allylic compounds show that the overall correlation is not substantially improved above that of the standard procedure: nonetheless, additional information on reaction characteristics is obtained with some substances.

Metabolism of a DDT metabolite via a chloroepoxide

The 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethene (DDT) metabolic intermediate 1-chloro-2,2-bis(p-chlorophenyl)ethene (DDMU) is partially metabolized in vivo by mice to 2-hydroxy-2,2-bis(p-chlorophenyl)acetic acid (alpha OH-DDA) and other metabolites which are excreted in urine. The subsequent DDT metabolic intermediates 1-chloro-2,2-bis(p-chlorophenyl)ethane (DDMS) and 1,1-bis(p-chlorophenyl)ethene (DDNU) are metabolized to alpha OH-DDA to a much lesser extent. These results imply that DDMU may be metabolized via an alpha-chloroepoxide. The authentic DDMU-epoxide, which after oral administration is excreted as alpha OH-DDA, is mutagenic in the Ames assay, and thermally rearranges rapidly to the corresponding alpha-chloroaldehyde, 2,2-bis(p-chlorophenyl)-2-chloroacetaldehyde (alpha Cl-DDCHO). As expected alpha Cl-DDCHO yielded the same urinary metabolites as DDMU-epoxide. This suggested metabolic pathway for DDMU via a chloroepoxide intermediate may account for the tumorigenicity of DDT in mice.