Recent experimental data on Extremely Low Frequency (ELF) magnetic field carcinogenic risk: open questions.

The NTP experimental studies on Extremely Low Frequency (ELF) magnetic fields (two-year studies in rats and mice and magnetic field promotion/DMBA initiation in female rats studies, NTP 1999) are of main interest because of the value and completeness of the information produced on neoplastic and non-neoplastic effects. Ajoint evaluation of the two-year study data indicates a thyroid C-cell focal hyperplasia increase in female rats at the same exposures at which the neoplasm increment of the same cells has been observed only in male rats (on which the "equivocal evidence" NTP classification is based). The significant exposure-related trichoepithelioma and trichoepithelioma plus other skin neoplasms reported for male rats in the two year studies finds some support in the female rat data relative to trichoepithelioma reported in incidence summary of the NTP 26-week initiation/promotion study, even if the experimental designs of the two studies are different. An indication of exposure-related increase of single mammary carcinomas emerges from the summary of neoplasm incidence, together with a dose-related decrease of mammary gland multiple carcinomas. A significant decrease of lung alveolar/bronchiolar adenoma incidence was observed in exposed groups in both mouse genders. It seems improbable to attribute the above effects only to chance. The present debate, dividing science in two opposite fields: one of them denying any appreciable carcinogenic effect of magnetic fields, and the other one hypothesising their dramatic effects, are presently devoid of reliable and exhaustive scientific support, which could only be provided by further research.

Carcinogenic risk assessment: some points of interest for a discussion.

This paper is aimed at providing some elements of discussion about points that emerge about the meaning of risk assessment procedures. The considerations that will be developed mainly pertain to four topics. First, the feasibility of objectively checking the validity of risk assessment results on the basis of epidemiological data, particularly for very low exposures. Second, the influence of uncertainty factors and the resulting variations in risk estimates. Third, the influence of individual susceptibility factors, easily entailing differences in risk in the order of three levels of magnitude. These differences, as a consequence of genetic factors, are often in the range of three orders of negritude and are more evident for low classes of exposure. In the general population, DNA repair related susceptibility should also be considered. Fourth, the mathematical model of the risk assessment procedure may itself influence the results. The default approach adopted by the US EPA is commented.

Developmental toxicity of carbendazim: comparison of no-observed-adverse-effect level and benchmark dose approach.

The benchmark dose (BD) approach has been applied to foetal data from four gavage segment II studies (rat studies 1 and 2, rabbit study, hamster study) on the teratogenic benzimidazole carbendazim. Nineteen parameters were assessed using the log-normal model as a practical tool to derive BDs; good model fitting was observed for all except two parameters. Data were evaluated on a 'per-implant/foetus' basis; BDs were derived from response rate increases of 1, 5, and 10%. The values were compared to the lowest-observed-adverse-effect levels (LOAELs) and no-observed-adverse effect levels (NOAELs) obtained by Fisher's exact test on a 'per-implant/foetus' basis. Frank effects observed only at the top dose and/or small sample size tended to increase the 95% confidence limits and this influenced the determination of BD. Generally, the BD approach provided slightly more conservative estimates than NOAEL; overall, BD01 and BD05 were similar to NOAEL, or even lower for several parameters. The LOAEL in most cases was similar to BD10. Reference doses obtained by dividing BD01 by a 10 or 100 uncertainty factor, corresponded to residual risks of 10(-5) or below. For two critical parameters (hydrocephalus in rat study 1 and resorption rate in the rabbit study) a NOAEL could not be found, whereas a BD was always determined.

Risk assessment of complex mixtures: some considerations on polycyclic aromatic hydrocarbons in urban areas.

The comparative examination of experimental and epidemiological data, together with risk evaluations concerning coke-oven, diesel, and gasoline motor emissions, as well as specific PAH fractions and single PAHs, indicates that, at least under risk additivity hypothesis, benzo(a)pyrene (B(a) may account for only a relatively small amount of the whole carcinogenic potential of PAH mixtures. This finding emerges from the comparison of risk evaluations of coke-oven and diesel emissions (based on epidemiological and/or experimental data) with risk evaluations of B(a)P as a single substance (based on carcinogenic bioassay data), as well as from the results of experimental studies evaluating the carcinogenic potency of motor exhaust condensates, of specific condensate fractions (particularly, the 4-7 ring PAH fraction), and of B(a)P. These data indicate that B(a)P might account for a percentage of the whole mixture carcinogenic response, at least in the hypothesis of an additive effect of PAHs. However, the overall carcinogenic response and risk still appear at least approximately related to the B(a)P concentration in the examined PAH mixtures. Finally, recent findings on PAH relative potencies (compared with B(a)P potency) indicate that several PAH present in mixtures commonly detected in occupational and in the general environment are characterized by a carcinogenic potency comparable with or even higher than that of B(a)P. This confirms the above hypothesis with respect to the significant, but minor role, of B(a)P. This relatively coherent picture appears to confirm that the reference to B(a)P as a complex mixture index may still represent a reasonable solution. However, the selection of a few other indicators from among the PAH whose relative concentrations and relative carcinogenic potencies are higher might improve the analysis.

Trihalomethanes in drinking water and cancer: risk assessment and integrated evaluation of available data, in animals and humans.

In our study, we attempted to jointly consider THM concentration data collected from drinking waters and carcinogenic risk assessment derived from mathematical models commonly used in this field (multi-stage models for laboratory animal experimentation data, and 'unit risk' derived from the relative risk in the case of epidemiological data). In order to estimate the risks related to joint exposure to different THMs, in this study the risk additivity hypothesis is taken into account. Based on animal data for the various tumors, carcinogenic risk estimates for different THM combinations vary from 2.7 x 10(-7) to 4.6 x 10(-6) per micrograms/l in relation to different carcinogenic substances published in the literature or specifically calculated in this study. The carcinogenic risk parameters derived from experimental studies and from epidemiological data were substantially consistent. Our study uses also as an example some data on concentration levels of THMs for drinking water supplies in Sardinia. The area mean THM concentration values for each supply varied, for ground waters, from 8.1 to 13.6 micrograms/l and, for surface waters, from 52.8 to 168 micrograms/l. For the 1976-1989 period, bladder cancer standardized mortality rates in the water distribution system areas where the THMs were measured indicate values similar, but generally lower, than the national ones, except in the province of Cagliari where the values were not significantly different. The risk estimates derived from animal studies are of the same order of magnitude as the epidemiological data in literature.

Crude oil spill in sea water: an assessment of the risk for bathers correlated to benzo(a)pyrene exposure.

In the spring of 1991, there was a shipwreck of the oil tanker "Haven" off the Ligurian coast of Italy. This resulted in the spillage of a very large amount of crude oil, some of which was burned off by fire. The accident caused several serious problems (sea and air pollution, damage to the marine fauna, risk of human exposure, etc.). In this context, an assessment was carried out at the Istituto Superior di Sanità with the aim of determining any possible risks to humans which might derive from bathing activities during the following summer season. The whole evaluation carried out after the accident demonstrated that the impacts induced were not serious enough to require bathing restrictions in the coastal areas involved. Assuming a benzo(a)pyrene (BaP) concentration in sea water of 1 microgram/m3 cancer risk is in the order of 10(-8) and in the case of 10-kg child, a 10(-6) risk level correspond to about 0.18 microgram/l of BaP in sea water.

The activity of the Istituto Superiore di Sanità in the field of existing chemicals.

The Istituto Superiore di Sanità (Italian National Health Institute, ISS) is one of the main Italian research institutes and a scientific body of the Italian National Health Service. At present, the ISS includes twenty laboratories, six technical services, an administrative division for personnel affairs and a library. The staff includes about 1400 people, plus over 600 external collaborators. The ISS international activities in the field of existing chemicals includes the participation in a wide number of programmes of the World Health Organization, the European Union, the International Agency for Research on Cancer, the Organisation for Economic Co-operation and Development and other organizations. At a national level, the ISS is particularly active in the field of risks connected with chemicals in the environment and in food, and constantly provides advice to the Ministry of Health and often to other ministries in the definition of laws and regulations which include technical-scientific aspects related to the existing chemicals. The ISS research activity in the field of chemical substances represents a significant part of the Environment research project, which includes more than one hundred research lines, and also of other research projects.

Heroin induces changes in mother-infant monkey communication and subsequent disruption of their dyadic interaction.

Heroin was given in a single, low dose (0.2 mg/kg i.v.) to the mother monkey of mother-infant pairs, living in a stable community of 30 individuals (Macaca fascicularis; six pairs treated plus six controls, in experiments repeated twice). The drug did not induce alterations in the response of the mother to the infant's calling signals when they were placed in a new environment denoting a potentially dangerous situation. However, after being returned to the community cage, the treated mother rarely responded to the infant's calling (non-alarming, non-vocal) signals (P less than 0.02). This behaviour was followed by an increased latency of the infant-to-mother approach, by a diminution of the reciprocal ventroventral clasping as well as a diminution of the overall duration of clasping, and by an increase in nipple suckling (unusual for the age), as compared to saline-treated controls (P less than 0.05, P less than 0.02, P less than 0.025, and P less than 0.05, respectively). Analysis of behavioural sequences strongly confirmed this relationship among data (P less than 0.01 and P less than 0.025). Even short lasting, pharmacologically induced failure in the non-vocal communication of a mother monkey may in itself constitute a pathogenetic mechanism. This is an important cause of the disruption of her dyadic interaction with the infant which consequently upsets the infant's behaviour.

Reproducibility of carcinogenic potencies estimated in different rodent species. Methylene chloride: a useful example.

The aim of this study was to investigate the reproducibility of carcinogenic potencies estimated by multistage model (and its linearized form) fitting to dose-response relationships referring to different rodent species and strains, different sexes, target organs and severity of prognosis. Methylene chloride represented a useful example since there were 11 single dose-response relationships available for the same administration route (inhalation) and for the above-mentioned variables. The multistage mathematical model and the 'linearized multistage' model (EPA's conservative procedure), which are the mainly adopted models for regulatory purposes, were used for the dose-response fitting of single trends and other different cumulative trends. The reproducibility of response frequencies at equal exposure doses was also analyzed. The mathematical function best describing each trend showed the constant presence of a linear component (for low doses) and, in the majority of cases, a quadratic second order component. Carcinogenic potencies were fairly consistent for the various parameters. A good interspecies reproducibility of carcinogenic potencies was observed. A high intraspecies reproducibility was also observed, even though obtained from different sexes, as well as varying degrees of severity of prognosis and, in the case of rats, different strains. The fluctuation of the estimated carcinogenic potencies was lower in mice than in rats.

Some endorphin derivatives and hydrocortisone prevent EEG limbic seizures induced by corticotropin-releasing factor in rabbits.

Corticotropin-releasing factor (CRF) injected into the cerebral ventricles of small mammals induces EEG limbic seizures, behavioral excitability, stereotyped behavior, and tardive enhancement of hippocampal theta voltage and frequency. Because we addressed this phenomenon when we explained the pathogenesis of infantile spasms in children, we wished to study the interference exerted by some gamma-endorphin fragments on EEG epileptiform and behavioral symptoms induced by CRF in the rabbit. Animals were implanted intracerebroventricularly (i.c.v.) with semichronic cortical and hippocampal electrodes, together with a cannula into the left lateral ventricle. When some gamma-endorphin derivatives (DT gamma E, DE gamma E) were injected intravenously (i.v.) for 4 days (or hydrocortisone once), they prevented the EEG ictal seizures induced in the hippocampus of rabbits by CRF injected i.c.v. Hydrocortisone and DE gamma E also prevented the appearance of scattered spiking and partially prevented tardive enhancement of theta voltage in the hippocampal EEG. Finally, DE gamma E also prevented stereotyped behavior and excitability induced by CRF. These results confirm the regulatory role exerted by CRF in limbic structure excitability and suggest that the above peptides may be involved in a regulatory feedback mechanism of CRF metabolism or activity. The possibility that these peptides may also have interesting antiepileptogenic properties should be considered.

The origin of DNA single strand breaks induced by ethylating agents in mammalian cells.

Chinese hamster ovary (CHO) cells were treated with two ethylating agents, N-ethyl-N-nitrosourea (ENU) and diethylsulfate (DES), and the kinetics of DNA single strand break (ssb) induction and rejoining were determined in parallel with DNA adduct formation and removal. In the case of DES, DNA ssb as determined by alkaline elution (AE) were repaired very slowly with more than 50% of the lesions still present on DNA 3 h after treatment. In contrast, 45% of ENU-induced ssb were repaired within 10 min. From the relative concentration of the different ethylated products and their repair rates as measured by high performance liquid chromatography (HPLC) analysis of the ethylated DNA, a theoretical function was constructed that describes the number of ssb expected at each time point after exposure to the mutagen. DES-induced ssb are explained by excision repair processes active on the ethylated purines, mainly 3-ethyladenine (3-EtAde) and 7-ethylguanine (7-EtGua). On the same basis, the rapidly repaired ENU-induced ssb remain unexplained. These results are also discussed in relation to the sensitivity of the two techniques, AE and HPLC, for detecting DNA damage.

Carcinogenic risk assessment: some comparisons between risk estimates derived from human and animal data.

Carcinogenic risk assessment may be based on epidemiological as well as experimental data; the aim of the present study is to compare these two procedures and to verify the efficiency of some animal bioassays for the prediction of tumor incidence and relative risk in man. The predictability obtained from animal models has been found to be fairly consistent with the data obtained from epidemiological studies.

Predictive value of serum aluminium levels for bone accumulation in haemodialyzed patients.

Uremic patients undergoing long-term dialysis risk accumulating tissue aluminium burdens and developing aluminium-related syndromes, such as dialysis encephalopathy and osteomalacia. A statistical retrospective study on 253 uremic subjects was carried out to verify the predictive value of serum aluminium levels on bone aluminium accumulation. Serum and bone samples collected at the same time were analyzed for aluminium content. Analyses were performed by graphite furnace atomic absorption technique. The results verified bone aluminium concentrations of less than or equal to 60 mg/kg d.w. (dry weight) in 144 patients and greater concentrations in 109 patients. The statistical discriminant analysis showed that serum levels can be predictive in aluminium bone accumulation (lower or greater than 60 mg/kg) with about a 7% margin of error. This value may be further reduced to about 2% if two threshold limits are used (53-81 micrograms/l). The specificity and sensitivity of the test were 89.6% and 83.5%, respectively.

The environmental behavior of chemicals in soil: atrazine as an example.

In this work a mathematical model has been developed and used to estimate the soil vertical distribution of Atrazine dispersed in the environment. Water transport, rise due to capillarity, and partition among soil-contained water, air, and organic matter, as well as degradation processes, are considered. As far as the vertical mobility in soil is concerned, the model has been derived from that proposed by P. H. Nichols, A. Walker, and R. J. Baker [1982). Pestic. Sci. 12, 484-494). Such a model has been extended to include a procedure which takes into account the Atrazine mobility due to gravitational water flow. The organic carbon (O.C.) concentration gradient in soil was also considered in the evaluation when assessing partition processes, according to models by P. J. McCall et al. [1983). Residue Rev. 13, 231-241) and D. McKay and S. Paterson [1982). Environ. Sci. Technol. 16, 12, 654). The degradation processes are assumed to be first order, linearly related with O.C. content in soil. The application of this model to two sets of soil data demonstrated that Atrazine requires a long time (2 years or more, depending on soil features) in order to percolate at a depth comparable with those of a groundwater source.

Exposure to agricultural treatment residues: some simple statistical considerations based on monitoring data for ethoxyquin on apples.

The data examined here concern ethoxyquin levels, mainly measured in apple samples from the retail market. In this study about three hundred measurements, carried out on apples in Northern-Central Italy and recently published, are examined, with the purpose of defining the main characteristics of value statistical distribution and variability and to optimize sampling criteria. The analysis did not indicate the presence of significantly high levels or consequently significantly high risks; nevertheless, it pointed out some important aspects in data collection and evaluation. First, it appeared that the statistical distribution of data is typically nonsymmetrical, non-Gaussian, and characterized by a tail extending toward the high values. The logarithmic transformation of data appeared useful in order to obtain a Gaussian distribution. As a rule, the data variability appeared to be high. The frequency and distribution of values above the analytical threshold resulted in significant change, both in time and in space. The percentage of positive values (above the analytical threshold) appeared to vary up to a factor of 2-3, as analogously did their geometric mean.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducibility of low-dose extrapolation procedure: comparison of estimates obtained using different rodent species and strains.

Carcinogenic risk assessment based on low-dose extrapolation of dose-response relationships is characterized by a significant level of uncertainty. The aim of this study was to investigate the reproducibility of risk estimates carried out using different animal species and strains. The Weibull and multistage mathematical modes, as well as the "linearized multistage" model (EPA "conservative" procedure), have been used for dose-response relationship fitting. Whenever necessary, the Michaelis-Menten function was introduced in the models to account for a possible metabolic process. The analysis was directed to dietary sodium saccharin and vinyl chloride inhalation carcinogenicity (nine total dose-response relationships). Data from different strains, species, and researchers were available for these substances. The general pattern of two sodium saccharin curves was an upward curve in both cases with a high consistency among parameters and risk estimates (the latter ranging within a factor 3). For vinyl chloride the trend was clearly downward for six carcinogenic dose-response relationships from different species; low-dose risk estimates, based on the upper confidence limits of the linear component, range within a factor 3. The study has indicated the reproducibility of the low-dose extrapolation process using different strains and species.

Dose-response relationships in rodents of promoter carcinogens: a tentative interpretation of some downward trends.

This study analyzes a set of dose-response curves relative to promoter carcinogens administered to experimental animals with or without initiator pretreatment. In the case of initiator plus promoter treatment, as well as for low experimental doses, the experimental data and their mathematical fitting indicate a downward shape of the dose-response curves as a general feature. In this study, the following hypothesis, according to the two-stage carcinogenic action of initiator plus promoter treatment, is presented to interpret this downward shape: (i) an initiating action, involving a subset of available "targets" (the number of "initiated" targets is assumed to depend on initiating treatment level), and (ii) a subsequent dose-dependent promoting process, mainly involving the initiated targets. This process reaches a saturation level when all the initiated targets have been promoted. This kind of process may be quantitatively described by a saturated exponential model: P(d) = K(1 - exp(-K0 + K1d)] which fits the experimental data fairly well. No indication supporting the hypothesis of a threshold for the chemicals examined resulted from the analysis. In the specific case of sodium saccharin, experimental dose-response relationships were available with or without initiator pretreatment (BBN and MNU). While in the first case the shape of the dose-response curve is downward, in the second case, it is upward and significantly different.

Animal species and strains used to test chemical carcinogens: results of a preliminary study.

The selection of animal species sufficiently representative of human physiological processes and sensitive to a wide spectrum of toxic agents is one of the major problems in toxicology. The aim of this study, based on animal experimental carcinogenesis data available from the literature, was the identification of animal strains most often used in experimental carcinogenesis. The analysis was limited to experiments on chemicals or groups of chemicals classified by IARC under Group 1 of carcinogenic risk (sufficient evidence). For each experiment considered in the study, data concerning animal species, strains, and substrains (whenever possible) were collected. The data analysis has shown that approximately 83 and 61% of the considered carcinogens were tested positively in mouse and rat, respectively, and that A, Swiss, and C3H mouse strains and Sprague-Dawley and Wistar rat strains were used most often. The study has shown that practically all decisions regarding the carcinogenicity of substances are based on the response of only two animal species (mouse and rat). Therefore, a clear and complete understanding of carcinogenicity mechanisms in these species becomes essential in order to extrapolate results to man.