The International Agency for Research on Cancer (IARC) published a monograph in 2015 concluding that glyphosate is "probably carcinogenic to humans" (Group 2A) based on limited evidence in humans and sufficient evidence in experimental animals. It was also concluded that there was strong evidence of genotoxicity and oxidative stress. Four Expert Panels have been convened for the purpose of conducting a detailed critique of the evidence in light of IARC's assessment and to review all relevant information pertaining to glyphosate exposure, animal carcinogenicity, genotoxicity, and epidemiologic studies. Two of the Panels (animal bioassay and genetic toxicology) also provided a critique of the IARC position with respect to conclusions made in these areas. The incidences of neoplasms in the animal bioassays were found not to be associated with glyphosate exposure on the basis that they lacked statistical strength, were inconsistent across studies, lacked dose-response relationships, were not associated with preneoplasia, and/or were not plausible from a mechanistic perspective. The overall weight of evidence from the genetic toxicology data supports a conclusion that glyphosate (including GBFs and AMPA) does not pose a genotoxic hazard and therefore, should not be considered support for the classification of glyphosate as a genotoxic carcinogen. The assessment of the epidemiological data found that the data do not support a causal relationship between glyphosate exposure and non-Hodgkin's lymphoma while the data were judged to be too sparse to assess a potential relationship between glyphosate exposure and multiple myeloma. As a result, following the review of the totality of the evidence, the Panels concluded that the data do not support IARC's conclusion that glyphosate is a "probable human carcinogen" and, consistent with previous regulatory assessments, further concluded that glyphosate is unlikely to pose a carcinogenic risk to humans.

During the past several years, concerns have been raised regarding the potential adverse effects of exposures to nonionizing radiation, particularly in the extremely low frequency (ELF) range (50 to 60 MHz) and radiofrequency radiation (RFR) with frequencies ranging from 30 KHz to 30,000 MHz. One focus of concern has been potential DNA interactions. Publications reviewing the genotoxicity of ELF radiation [McCann et al. (1993): Mutat Res 297(1):61-95; Murphy et al. (1993): Mutat Res 296:221-240; NAS (1997)], have been uniform in concluding that the weight of evidence does not indicate any genotoxic risk from exposure to this type of radiation. Concern that RFR may be associated with adverse biological effects [WHO, 1993], including recent allegations that they may be involved in the production of brain tumors in humans [Elmer-Dewit (1993): Time, February 8:42], has resulted in the production of a large number of publications describing the effects of RFR on the integrity of nucleic acids. Data from studies conducted in a frequency range from 800 to 3,000 MHz were reviewed and subjected to a weight-of-evidence evaluation. The evaluation focused on direct toxicological effects of RFR as well as on studies addressing basic biological responses to RFR at the cellular and molecular level. The data from over 100 studies suggest that RFR is not directly mutagenic and that adverse effects from exposure of organisms to high frequencies and high power intensities of RFR are predominantly the result of hyperthermia; however, there may be some subtle indirect effects on the replication and/or transcription of genes under relatively restricted exposure conditions.

Laxative senna products and several of their specific components have been submitted to a large number of genetic tests. While most studies gave negative responses, results from some of the studies suggest that components of senna products, particularly emodin and aloe-emodin, have genotoxic activity. Assessment of the genotoxicity profile of these substances, in light of other data from animal and human metabolism or kinetic studies, human clinical trials and rodent carcinogenicity studies do not support concerns that senna laxatives pose a genotoxic risk to humans when consumed under prescribed use conditions. Environ. Mol. Mutagen. 29: 1–9, 1997 © 1997 Wiley-Liss, Inc.

Laxative senna products and several of their specific components have been submitted to a large number of genetic tests. While most studies gave negative responses, results from some of the studies suggest that components of senna products, particularly emodin and aloe-emodin, have genotoxic activity. Assessment of the genotoxicity profile of these substances, in light of other data from animal and human metabolism or kinetic studies, human clinical trials and rodent carcinogenicity studies do not support concerns that senna laxatives pose a genotoxic risk to humans when consumed under prescribed use conditions.

The development of transgenic animals has already had a significant impact in biomedical research. Non-human models of human diseases (i.e., sickle cell disease, cystic fibrosis and AIDS) have been produced in mice and are being used to screen potential therapies (Breslow, 1994). Domesticated animals genetically engineered to: (a) resist disease, (b) produce meat or eggs with less cholesterol, or (c) accelerate growth may be introduced into agriculture in the near future (Sedlak, 1989). Transgenic animals have also been proposed as living bioreactors for the commercial production of pharmaceuticals and other biologicals not easily synthesized by other methods (Van Brunt, 1988).

The Environmental Mutagen Society (EMS) was one of the first professional scientific societies organized to respond to an environmental concern. The threat of environmental pollution stimulated the formation of the organization in 1969. The Society's mission was to create a forum for discussion of methods and strategies to deal with mutagenic agents formed and/or released into the environment. During the past 25 years, EMS has provided a forum for innovation and scientific discussions. The Environmental Mutagen Society, and, in particular, its applied role in genetic toxicology, has had a profound positive impact on many disciplines in toxicology and safety assessment (i.e., carcinogenesis and invitro alternatives). (C) 1994 Wiley-Liss, Inc.

The Environmental Mutagen Society (EMS) was one of the first professional scientific societies organized to respond to an environmental concern. The threat of environmental pollution stimulated the formation of the organization in 1969. The Society's mission was to create a forum for discussion of methods and strategies to deal with mutagenic agents formed and/or released into the environment. During the past 25 years, EMS has provided a forum for innovation and scientific discussions. The Environmental Mutagen Society, and, in particular, its applied role in genetic toxicology, has had a profound positive impact on many disciplines in toxicology and safety assessment (i.e., carcinogenesis and in vitro alternatives). © 1994 Wiley-Liss, Inc.

Among the array of protective mechanisms is that of antioxidants. Endogenous antioxidants include ascorbate, urate, a-tocopherol, andalbumin-bound bilirubin, Frie et al., (1988). In addition to these endogenous agents, there are phenolic derivations widely distributed among plant species which constitute an exogenous source of antioxidants, Stich (1991). Synthetic antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BRT) and phydroxybenzoic acid (pHBA) plus some of the naturally occurring phenolic antioxidants are usedextensively in thepreservation of food products.

A transgenic mouse strain with a high copy number of rescuable lacZ sequences was evaluated for its effectiveness in detecting lacZ- mutations in selected tissues. Procarbazine, cyclophosphamide, ethylnitrosourea, 7,12-dimethylbenz[a]anthracene (DMBA), acrylamide and chlorambucil were tested following either single or repeated dosing regimens. Bone marrow, liver, skin and testis tissues were selected to assess as target sites for mutation. Bone marrow, liver and testis tissues were examined for mutation following exposures to ethylnitrosourea and chlorambucil. Increased mutant frequencies were found for both chemicals in all three tissues. Bone marrow tissue was examined for mutation following procarbazine, cyclophosphamide and acrylamide exposures, and skin was examined for mutation following dermal application of DMBA. Mutation induction was observed in all cases. The results obtained from this investigation demonstrate the applicability of this transgenic mouse as an effective model to detect and analyze gene mutation in selected organs including germinal tissues. Studies of organotrophic chemical mutagens and carcinogens are possible with this model as are studies of the susceptibility of germinal tissues to mutagen exposures.

The genotoxicities in vitro and in vivo of the mouse-skin carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) have been compared with those of its weakly carcinogenic 4,5-sulphyr analogue, 6,11-dimethylbenzo[b]naphtho-[2,3-d]thiophene (S-DMBA). The only datasets that correlated with the relative carcinogenicity of these agents to the skin were those conducted using topically exposed mouse skin. Thus, both chemicals induced lacZ− mutations in the skin of lacZ+ transgenic mice, and both produced DNA adducts on mouse-skin DNA as assessed using the 32P-postlabeling technique. In each case, DMBA gave a stronger response than did S-DMBA. In contrast to these responses, only DMBA was active in the mouse bone-marrow micronucleus assay and in the C3H10T1/2 in vitro cell transformation assay. Both chemicals were mutagenic to Salmonella and of approximately equal potency. The molecular geometry of DMBA and S-DMBA are compared, and divergent CASE predictions of activity in the Salmonella assay and skin-painting bioassay are discussed. The importance of conducting predictive genotoxicity assays in systems close to those in which carcinogenicity is to be assessed is emphasized by these data.

The genetic toxicology databases for chemicals that have been tested extensively are generally composed of inconsistent responses from a diverse set of assays. Consequently, difficulties arise when the data are evaluated for classifying the agent or for assessing the chemical's hazard potential. Several years ago, the International Commission for Protection against Environmental Mutagens and Carcinogens (ICPEMC) established a committee to construct a process for compiling and interpreting diverse data sets. The Committee has developed a weight-of-evidence approach that combines test data into a series of scores for test type, class, family, and a consensus score defining the relative mutagenic activity of the agent compared with other chemicals in the database. This report describes the method and preliminary results from 113 chemicals.

The alkylating agents methyl methanesulphonate (MMS) and ethyl methanesulphonate (EMS) have non-linear dose–response curves, with a no-observed effect level (NOEL) and a lowest observed effect level (LOEL) for both gross chromosomal damage and mutagenicity. However, the biological mechanism responsible for the NOEL has yet to be identified. A strong candidate is DNA repair as it may be able to efficiently remove alkyl adducts at low doses resulting in a NOEL, but at higher doses fails to fully remove all lesions due to saturation of enzymatic activity resulting in a LOEL and subsequent linear increases in mutagenicity. We therefore assessed the transcriptional status of N-methylpurine-DNA glycoslase (MPG) and O6-methylguanine DNA methyltransferase (MGMT), which represent the first line of defence following exposure to alkylating agents through the respective enzymatic removal of N7-alkylG and O6-alkylG. The relative MPG and MGMT gene expression profiles were assessed by real-time RT-PCR following exposure to 0–2 μg/ml MMS for 1–24 h. MPG expression remained fairly steady, but in contrast significant up-regulation of MGMT was observed when cells were treated with 0.5 and 1.0 μg/ml MMS for 4 h (2.5- and 6.5-fold increases respectively). These doses lie within the NOEL for MMS mutagenicity (LOEL is 1.25 μg/ml), thus this boost in MGMT expression at low doses may be responsible for efficiently repairing O6methylG lesions and creating the non-linear response for mutations. However, as the LOEL for MMS clastogenicity is 0.85 μg/ml, O6-alkylG is unlikely to be responsible for the clastogenicity observed at these concentrations. Consequently, at low doses N7-methylG is possibly the predominant cause of MMS clastogenicity, while O6-methylG is more likely to be responsible for MMS mutagenicity, with MGMT up-regulation playing a key role in removal of O6-alkylG lesions before they are fixed as permanent point mutations, resulting in non-linear dose–responses for direct acting genotoxins.

The genetic toxicity of atrazine, a member of the s-triazine herbicides, was reviewed with the objective of classifying the chemical. Atrazine has been subjected to a broad range of genetic tests with predominantly negative results. Some publications, specifically those measuring dominant lethality in mice and bone marrow clastogenicity in rodents, reported conflicting results across two or more independent tests. Two approaches were employed to evaluate and interpret the results. The first approach attempts to classify each type of genetic endpoint as positive or negative and resolve test conflicts by critical assessment of the study and detailed data. This is the more traditional “expert judgment” approach to hazard assessment. The second approach employs a computer-assisted weight-of-evidence method of data analysis. This approach does not require resolution of conflicts but uses all data sets to arrive at a classification of hazard. The first approach was able to resolve some conflicts but not all. Use of the “expert judgement” results in an equivocal conclusion and classification. Use of the weight-of-evidence method resulted in a conclusion that atrazine does not pose a mutagenic hazard. The weight-of-evidence scheme is proposed to be a more practical and relevant approach for assessing complex data sets.

The inherent or added capability for metabolism of chemicals to activate or inactivate intermediates has been a key in development of most of the tests used in genetic toxicology. The addition of an exogenous source of metabolism in the form of cell-free enzymes and their cofactors has aided in the design of most in vitro methods since 1971. Although it appears that this type of metabolic system will continue to be widely used in the future, new and potentially very useful techniques for carrying out metabolism will be added to those currently in use.

Calcium cyclamate and its major metabolite cyclohexylamine have been subjected to numerous evaluations for genetic activity. With the exception of studies for chromosome damage, the results have been negative. Results from a wide range of in vitro and in vivo cytogenetic assays ranged from clearly negative to various degrees of clastogenicity. Interpretation of the cytogenetic studies has been complicated by the conflicting responses, although some of the positive effects seem to be the consequence of secondary effects produced by high ion levels and excessive toxicity. In the studies presented here calcium cyclamate and cyclohexylamine were tested for mutagenic activity using an in vitro mammalian cells assay for gene mutation and an in vitro unscheduled DNA synthesis assay in rat hepatocytes with the Drosophila sex-linked recessive lethal assay. Calcium cyclamate was not genetically active in any of the three assays when tested to the maximum possible concentrations. The compound was largely nontoxic but did show some evidence of cytotoxicity in rat hepatocytes at concentrations of 1 mg/ml and higher. Cyclohexylamine was also negative in the three assays, but was considerably more cytotoxic at the concentrations used. The results from the three studies conducted in this evaluation are in general agreement with the majority of published genetic toxicology data for these two chemicals and indicated that the calcium cyclamate and cyclohexylamine have no direct, intrinsic genotoxicity of the type measured by these assays.

The inherent or added capability for metabolism of chemicals to activate or inactivate intermediates has been a key in development of most of the tests used in genetic toxicology. The addition of an exogenous source of metabolism in the form of cell-free enzymes and their cofactors has aided in the design of most in vitro methods since 1971. Although it appears that this type of metabolic system will continue to be widely used in the future, new and potentially very useful techniques for carrying out metabolism will be added to those currently in use.

Determining the genetic hazard of a chemical is generally approached by using an assortment of tests for measuring the DNA reactivity of a chemical or its resultant genotoxicity. Over 100 short-term tests employing a wide diversity of species and genetic mechanisms have been used to measure genetic hazard. To date, attempts to achieve a standard test battery for defining genetic hazard have not been successful. Consequently, testing for genetic hazard involves the use of test batteries with variable types and numbers of assays. This increases the difficulties of interpreting data sets since the data sets are often filled with inconsistent responses from diverse types of assays. Several years ago, the International Commission for Protection Against Environmental Mutagens and Carcinogens (ICPEMC) established a Committee to develop a method to compile and interpret diverse short-term test data. The Committee has produced a quantitative weight-of-evidence approach that combines test data using certain parameters such as dose, replication, and metabolic capacity into a series of scores for test type, test class, test family, and an overall score that defines the total weight-of-evidence regarding the genetic hazard of the agent. A description of the method and results from the evaluation of selected chemicals is provided.