Non-carcinogenic Substances Research Articles

Derivation of Risk Management Criteria for Chemicals of Unknown Toxic Potency at Contaminated Sites

Environmental investigations of former industrial sites often detect the presence of chemicals for which no soil criteria exist and for which regulatory agencies have not derived estimates of toxic potency. This poses a considerable problem for making informed risk management decisions involving sites where such chemicals are present. As a result, a methodology has been developed for making risk-based decisions for chemicals of unknown toxic potency in soil at contaminated sites. The method is based on principles and procedures used by the US Food and Drug Administration (USFDA), the US Environmental Protection Agency (USEPA) and the Canadian Council of Ministers of the Environment (CCME). After analyzing the data on hundreds of carcinogenic and non-carcinogenic substances, the USFDA and other leading researchers have concluded that, if no toxicological data is available on a chemical, exposures less than 1.5 µg/person/day (i.e., 0.02 µg/kg body weight/day) are unlikely to result in appreciable health risks even if the substance was later found to be a carcinogen. To develop maximum soil concentrations that will be protective of human health (i.e., Risk Management Criteria or RMC), the above exposure limit of 0.02 µg/kg body weight/day has been assumed to be protective of risks from exposure to chemicals lacking toxicological data. Using a stochastic risk assessment model for estimating exposures to chemicals from contaminated sites, our analyses indicate that a soil concentration of 2 µg/g would be protective of human health for land uses that include residential, commercial, and industrial development provided no major indirect pathways exist at the site. If indirect pathways exists (e.g., vapor infiltration of soil gases, uptake of chemicals into garden produce, etc.), alternate RMC could be developed, that include such indirect pathways, using the methodology provided in this paper. Used by experienced risk assessors, the approach is a scientifically defensible screening method that will preclude many chemicals from unnecessary evaluation, while allowing risk assessors to focus efforts on chemicals of greater concern and make informed risk management decisions.

Limit Value Assessment for Respirable Coal Mine Dust in Germany

Abstract Occupational limit values for airborne noncarcinogenic substances are defined as threshold limit values in Germany. This concept presumes a “hockey stick” relationship between mean shift concentrations and health effects. A population-based threshold limit value (in Germany called the MAK value) is defined as the maximum value on the exposure scale below which a constant baseline risk is observed. This concept was originally developed for toxic substances and is modified to handle the case of fibrogenic dust exposure. The incidence of profusion category 1/1, International Labor Organization (ILO) 1980 of coal workers' pneumoconiosis (CWP) is used as the outcome measure to evaluate the health effects of respirable coal mine dust. The basic concept is modified firstly to analyze the dependence of disease incidence on the mean long-term concentration, allowing for linear and nonlinear effects of time since first exposure, and secondly to handle incomplete clearance in terms of a time-dependent thres...

Reference dose (RfD): Description and use in health risk assessments

For many years the concept of the “acceptable daily intake” has served the toxicological and regulatory fields quite well. However, as approaches to assessing the health significance of exposures to noncarcinogenic substances receive greater scrutiny, some difficulties with this traditional approach have become more apparent. Consequently, the concept of the “reference dose” is introduced in order to avoid use of prejudicial terms (e.g., “safety” and “acceptable”), to promote greater consistency in the assessment of noncarcinogenic chemicals, and to maintain the functional separation between risk assessment and risk management.

Carcinogenesis in Mammalian Urothelium: Changes Induced by Non-Carcinogenic Substances and Chronic Indwelling Catheters

Carcinogenesis in urinary bladders may not be represented by a continuum of pathological lesions beginning with papillary tumors or flat dysplasias/atypias. In a previous experiment, sterile water and saline continuously infused via catheters connected to ALZA mini-pumps were shown to induce papillary urothelial lesions indistinguishable from tumors considered to be carcinomas in most histological classification schemes. The animals in the initial experiment were followed for relatively brief periods which did not allow for determination of potential reversibility of the process and did not distinguish the effects of the catheters versus those of the infused substances. The present study was designed to control for these variables. Rats were divided into seven groups to examine the urothelial changes after: 1) surgery alone, 2) continuous infusion of the sterile water and mitomycin C, and 3) chronic indwelling catheters with and without infusion. The results indicated that chronic irritation with indwelling catheters was a strong stimulus for the induction of urothelial neoplasms and that continuous infusion of certain substances, even sterile water, might play a small role in the process of carcinogenesis. Comparing the frequencies of papillary urothelial tumors appearing after brief exposure to sterile water and catheters in the initial experiment (75 per cent) and papillary lesions appearing long after removal of the sterile water and catheters in the current study (0 per cent) indicates that these lesions are reversible and probably not neoplastic.

Bladder cancer induced by noncarcinogenic substances.

Chemical carcinogenesis is currently regarded as a complicated series of events requiring initiation and promotion in specific sequences. Carcinogens are thought to be chemicals which can induce both initiation and promotion so that few if any additional host or environmental factors are required in the production of neoplasms. Most experimental studies to date have investigated bladder cancer using these highly active agents and the role of other substances in urothelial neoplasia has not been emphasized. We have examined the role of a variety of solutions, including water and saline, in pilot studies of urothelial carcinogenesis using the ALZA mini-pump for continuous infusion. Bladder tumors indistinguishable morphologically from papillary transitional cell carcinomas were induced. Although experimental induction of bladder cancer with powerful carcinogens may completely overwhelm host defenses and result in more and higher grade neoplasms, similar tumors may occur after exposure to substances not generally considered to be carcinogenic. This process, which probably requires cofactors and host-chemical interaction, may be more representative of environmental carcinogenesis than systems using powerful carcinogens and should be further investigated.

Further studies on the inhibition of chemical carcinogenesis by Corynebacterium parvum

The conditions under which administration of Corynebacterium parvum (CP) inhibits the development of tumours in response to methylcholanthrene (MC) have been further delineated. After subcutaneous (SC) injection of a single large dose of MC in solution (0.5 mg to CBA mice, 0.25 mg to BALB/c), repeated intravenous (IV) injection of CP starting 4 days before injection of the carcinogen delays or prevents the development of fibrosarcomas, whereas a similar course of injections starting 4 weeks later, and single injections of CP at various times, have little or no inhibitory effect. After injection of only 0.1 mg MC repeated injection of CP, even when started before injection of carcinogen, is ineffective. Carcinogenesis may also be inhibited by repeated IV injection of CP starting 4 days before implantation of Millipore discs impregnated either with MC alone or with a mixture of MC and paraffin wax. In untreated mice SC implantation of a disc impregnated with 0.1 mg MC was more strongly carcinogenic than SC injection of the same quantity of MC in solution. The effect of CP depended on the site of implantation, the type of disc and the regimen of CP administration. With MC wax discs implanted in the peritoneal cavity the development of tumours was completely prevented by repeated administration of CP starting before insertion of the disc. Similar treatment resulted in more modest inhibition of carcinogenesis after SC implantation of MC wax discs and MC discs of small pore size. In previous papers three possible mechanisms have been suggested to account for the inhibitory effect of CP on chemical carcinogenesis by MC: (1) destruction of transformed cells by CP-activated macrophages; (2) accelerated conversion of the MC to completely non-carcinogenic substances; and (3) inhibition of the conversion of MC to a highly carcinogenic epoxide. The present results do not exclude any of these possibilities but the observation that single injections of CP have little effect suggests that modification of the metabolism of MC is not the whole explanation. The different results obtained with carcinogenic discs implanted in different sites, and with different types of disc, are attributed to differences in the degree of macrophage activation and in the extent to which activated macrophages made effective contact with the carcinogen and with developing tumour cells. Two possible explanations of the failure of repeated injection of CP to reduce the incidence or rate of development of tumours in response to injection of only 0.1 mg MC are suggested.

Choline Deficiency, Partial Hepatectomy, and Liver Tumors in Rats and Mice.

Choline deficiency (CD) increases susceptability of (he rat liver to a number of hepatocellular carcinogens with a wide diversity of structure and potency. While severe CD results in micronodular cirrhosis and enhanced tumor induction, even a mild deficiency, without cirrhosis is sufficient to result in the increased carcinogenic response. The effects of CD are in part mediated via modulation of microsomal and, possibly, cytosolic enzymes responsible for activation/deactivation of carcinogens. The B6C3F1 hybrid mouse is remarkably sensitive to initiation/promotion of liver tumors by many substances or conditions. Choline deficiency or partial hepatectomy alone, or in concert, markedly enhances liver tumor induction in the absence of any known carcinogen. These data indicate that the liver of this strain of mouse is "initiated" at or shortly after birth and can be promoted by non-carcinogenic substances or conditions.

DNA alteration and repair

DNA alteration and repair is undoubtedly as essential stage in the mechanism of chemical carcinogenesis. Present knowledge has in fact shown, and in a rather convincing manner, that the majority of known chemical carcinogens, in addition to radiations and viruses, are also mutagens in the widest sense of the word and usually induce alteration of the genome. Proof that carcinogenic or procarcinogenic chemical agents display muta.genic action is based on the recent experiments by McCann and Ames (4), who demonstrated a close relationship betneen carcinogenicity and mutagenicity in 9OcTo of the tested products (157/ 173, whereas the percentage of non-carcinogenic substances which were also non-mutagenic was 8770 (94/108) (Fig. 1). Initial experimental data allso confirm that failure of DNA repair could result in the appearance of tumours: for example, the potentiation of the oncogenic action of ultraviolet radiations in patients suffering from Xeroderma Pigmentosum who show a defect in DNA repair, in the same way as Cleaver (1) has ascertained recently for Ataxia Telangiectasia and Cokayne’s syndrome. At this point it is perhaps necessary to try to understand why alterations in nuclear DNA should be considered as the basic mechanism of carcinogenesis induced by chemical agents, when interaction has certainly been observed between the latter and other molecules involved in gene expression, such as RNA or regulating proteins. The possibility of chemical interactions between damaging agents and other target molecules has in fact already been shown in the literature. Two examples can be quoted: Wunderlich et al. (9. 10) observed a mcthylation of the mitochondrial DNA by methylnitrosourea (MNU) or dimethylnitrosamine (DMN); and the experiments by Sarma et al. (5) on the relationship between carcinogens like 2-AAF, MNU and ethionine and some types of RNA. In our view.

Synergistic effects of N-nitroso compounds in experimental long-term carcinogenesis studies.

Combination effects in chemical carcinogenesis can be described either as syncarcinogenesis action of two or more carcinogens or as modified effects of noncarcinogenic substances on the action of carcinogens. Combination experiments in which one or more carcinogenic N-nitroso compounds are administered to experimental animals together with other cancer-inducing or noncarcinogenic xenobiotics show that in animal experimental animals together with other cancer-inducing or noncarcinogenic xenobiotics show that in animal experiments independent activities, additive effects, and synergistic actions as well as inhibitions may occur. After the administration of several carcinogenic substances predominantly additive effects were observed so far. A large number of experiments demonstrate the influence of different modifying xenobiotics on the action of chemical carcinogens. It is shown that in animal experiments there are real synergistic and inhibitory effects of noncarcinogenic compounds of different chemical structure on the action of chemical carcinogens. As far as the mechanism of action can be made plausible, these are either enzyme-inducing or enzyme-inhibiting effects, competitive or noncompetitive inhibitions of substrates on the enzymes, or alterations of the rate of cell division and correspondingly of the cell-specific protein synthesis. Before establishing acceptable risk values for individual chemical carcinogens it should be taken into account that as a rule interactions are to be expected in man.

Bladder Cancer and Squamous Metaplasia in Spinal Cord Injury Patients

The influence of long-term indwelling urethral catheterization was studied by random bladder and urethral biopsies in 62 spinal cord injury patients. Six patients (10 per cent) had diffuse squamous cell bladder carcinoma, 4 of whom had no tumor visible endoscopically. Five of the patients with cancer were among 25 patients (20 per cent) managed with an indwelling urethral catheter for more than 10 years (average 21 years, range 15 to 30 years). The other cancer patient had been free of the catheter for 27 years after suprapubic cystotomy for 4 years. Gross and microscopic hematuria was associated with cancer. Squamous metaplasia of the bladder was significantly greater in patients who had been catheterized for more than 10 years (80 per cent), compared to those catheterized for less than 10 years (42 per cent) and patients without catheters (20 per cent). Urethral squamous metaplasia increased slightly in long-term catheterization patients. Urinary infection was universal and did not distinguish patients with inflammation, metaplasia or cancer. Therefore, the duration of indwelling catheterization seems to be the major factor in squamous changes in these patients.

Carcinogenic Risk Assessment

Carcinogenic risk assessment involves a mixture of statistical, scientific, and public policy considerations. Concepts in current use, such as "no observed effect levels" and "virtual safety," and the problems in implementing them by means of dose-response models, particularly the probit-log dose and linear models are reviewed. The upper limits to risk provided by some conservative procedures are inconsistent with coherent balancing of risks and benefits. A common basis to the dose-response curves describing both carcinogenic and noncarcinogenic effects is to be found in deactivating reactions. A simplified model in which a toxic substance is activated and deactivated in separate and simultaneous reactions is presented and the dose response curve implied by the model is deduced. This curve has the general form of a hockey stick, with the striking part flat or nearly flat until the dose administered saturates the deactivation system, after which the probability of a response rises rapidly. Such a curve describes the Bryan-Shimkin methylcholanthrene-tumor incidence dose response curve as well as the probit log-dose model. The concept of a saturation dose is relevant to risk assessments for carcinogenic and noncarcinogenic substances alike.

The action of a single toxic dose of 2-acetylaminofluorene or allylic alcohol on the adrenals: II. Effect on adrenal cyclic 3′,5′-adenosine monophosphate concentration during the 1st and 2nd day

In the adrenals of male Sprague-Dawley rats the concentration of cyclic 3',5'-adenosine monophosphate (cAMP) was studied 5, 10, 14, 24, 30 and 39 hours after single intoxication by 2-acetylaminofluorene (AAF) or allylic alcohol (ALL). Beside diurnal changes a transient elevation of adrenal cAMP concentration occurred when compared with the controls 10 hours after intoxication. Thereafter, up to the 30th hour of investigation the values of the experimental groups as well as those of the control groups were within the same range. In the final stage of the experiment (30-39 hours after application) ALL intoxication was associated with a significant increase in adrenal cAMP concentration whereas it was reduced to subnormal level following AAF intoxication. In an earlier experimental study (Danz et al. 1976) we found inverse behaviour of the proliferative activity in the adrenal cortex: cell division was intensified by AAF whereas ALL was ineffective. These results indicate that division growth and functional activities are alternating conditions also in the adrenals. The possible causes of the different effects of intoxication by carcinogens or by noncarcinogenic substances are discussed.

The proliferative activity of the adrenal cortex as influenced by carcinogenic and noncarcinogenic substances

A single oral toxic dose of carcinogens (N-nitrosomorpholine, aflatoxin B1, N--methyl-N-nitrosourea, urethan) causes a significant increase of the mitotic rate in the adrenal cortex 48 hours after application. Both, the control animals (water via stomach tube) and the animals treated with acetylsalicylic acid, arsenic, phenol and actinomycin D do not produce this effect. These findings confirm our previous results obtained by administration of acetylaminofluorene, diethylnitrosamine, dimethylnitrosamine and trinitroso-trimethylen-triamine. It is possible that the increased mitotic activity of the adrenal cortex is correlated with the substances applied.

Experimental investigations on immunodepressive properties of carcinogenic substances in male Sprague-Dawley rats.

The finding during the nineteen-fifties that carcinogens depress the immune response led to the hypothesis that the rise of malignomas might be correlated with the impairment of the immunocompetent system (1–3). This hypothesis was confirmed by systematic investigations of these relationships by STJERNS-WARD, and especially by the comparison of the activities of carcinogenic and noncarcinogenic hydrocarbons, which revealed that in contrast to noncarcino-genic substances, carcinogens caused immunosuppression (4–6).

Differential chromosomal effects of carcinogenic and noncarcinogenic substances: An experimental study on the mouse

In the mouse, lesions resembling carcinoma in situ are induced by repeated topical application of methylcholanthrene and podophyllin. Methylcholanthrene is a known carcinogen, podophyllin is not. The present study was undertaken to compare the chromosomal effects of these substances. A single application of methylcholanthrene induced no discernible differences when compared with controls. A single application for podophyllin produced numerous mitotic figures. All but two were metaphases and all nuclei contained the species chromosome number. Among the animals receiving repeated methylcholanthrene applications, most chromosomes appeared morphologically identical to the controls; however, a number of metaphase figures had grossly distorted chromosomes and appeared dead or dying or entirely beyond the usual mitotic controls. Among the animals receiving repeated podophyllin applications a large number of nuclei contained twice the species chromosome number (80). Chromosome coalescence was found only in this group and probably is the phenomenon responsible for the malignant appearance of podophyllin-treated cells.

The Sulfhydryl Group and Carcinogenesis

This chapter examines the reactions of carcinogens with sulfhydryl group (SH) groups in vivo and in vitro . Normal cell division and growth have been found to be associated in some organisms with a SH-SS cycle, which can be modified by SH compounds and certain SH-reacting substances. The chapter also discusses the de novo synthesis of glutathione (GSH) and certain SH containing acid-soluble materials during the SH-SS cycle. Because growth inhibition is a characteristic property of certain carcinogens, both growth inhibition and the interaction between carcinogens and SH groups are discussed in the chapter in relation to systems associated with cell division and growth. The carcinogenic process may occur in three stages: (1) the inhibition of cell division through the interaction of carcinogen with critical SH groups, (2) an over compensatory response to the inhibition of cell division, and (3) a subsequent and permanent loss of control of cell division. This sequence of events could occur by feedback adjustment after the initial reaction of carcinogens with particular SH compounds. Physical and chemical carcinogens under certain conditions markedly inhibit the growth of animals, tumors, and cells. It is possible that these effects may be due to the interference with SH functions in the control of cell division. The growth-inhibitory action of the carcinogenic polycyclic aromatic hydrocarbons may result (1) from a general systemic suppression of GSH synthesis by a direct action of the carcinogens on GSH synthetases or on some other point in the synthesis of GSH, or (2) from an interference in the hormonal control of GSH synthesis for the whole body, in which process growth hormone may play some key part. Carcinogenic hydrocarbons have growth-stimulatory effects that, in general, arc not found in noncarcinogenic substances.