Epidemiological studies in humans

Group A5 Not suspected as a human carcinogen. Trichloroethylene is not suspected to be a human carcinogen on the basis of properly conducted epidemiologic studies in humans. 

Epidemiological studies in humans do not suggest an association between excess exposure to selenium and cancer." Low levels of intake, however, have been associated with an increased risk of developing many kinds of cancers. With the exception of selenium sulfide, most animal studies have shown that selenium compounds inhibit tumorigenesis." High doses of selenium sulfide administered by gavage caused liver tumors in rats and lung... 

Well documented observational, clinical and epidemiological studies in humans provide more direct information on human health effects than do studies in animal systems. However, the number of such human data is limited, and in many cases animal data are the only information available on potential adverse reproductive effects. 

Aflatoxins are products of species of the genus Aspergillus, particularly A flavus, a common fungus found as a contaminant of grain, maize, peanuts, and so on. First implicated in poultry diseases such as Turkey-X disease, they were subsequently shown to cause cancer in experimental animals and, from epidemiological studies, in humans. Aflatoxin Bl, the most toxic of the aflatoxins, must be activated enzymatically to exert its carcinogenic effect. 

The available data do not indicate that aluminum is a potential carcinogen. It has not been shown to be carcinogenic in epidemiological studies in humans, nor in animal studies using inhalation, oral, and other... 

Extensive long-term animal feeding studies and epidemiological studies in humans have failed to show any evidence that cyclamate is carcinogenic or mutagenic. As a result, sodium cyclamate is now accepted in many countries for use in foods and pharmaceutical formulations. See also Section 16. 

Excess radiation-induced cancers have also been demonstrated in well-controlled studies using laboratory animals (e.g., mice, rats, and dogs). The data from animal studies are being used to supplement the dose-response information obtained from epidemiological studies in humans and are providing model systems for the investigations of the mechanisms of radiation-induced diseases such as cancer. 

Interest in vitamin A and its synthetic analogs as a potential factor in the prevention and treatment of certain types of cancer has been growing. In addition, there is evidence that vitamin A may be related to pollutant toxicity. Recent epidemiological studies in humans with a sample of 8000 men in Chicago showed a low lung cancer incidence in those with a high vitamin A level in the diet, while the incidence was higher in those people with a low dietary vitamin A. Experimental studies show that rats exposed to PCB, DDT, and dieldrin caused a 50% reduction in liver vitamin A store. In another study, rats deficient in retinol were shown to have a lowered liver cytochrome P-450 activity. The effect of vitamin A deficiency on MFO enzymes, however, depends on several factors such as substrate, tissue, and animal species. 

Acute toxicity may result from tfie ingestion of cadmium. Symptoms that follow cadmium ingestion may include abdominal pain, nausea, and vomiting symptoms that follow inhalation include acute respiratory irritation and/or inflammation. Epidemiologic studies in humans have found associations between cadmium exposure and lung cancer, and between cadmium exposure and prostate cancer. Other evidence of the carcinogenic potential of cadmium has been found in the results of animal studies, see also Toxicity. 

Chronic oral exposure data from epidemiological studies in humans indicate that the LOAEL (lowest observable adverse effect level) for skin lesions and other effects is probably about 10-20 pgkg per day, and that the NOAEL (no observable adverse effect level) is probably between 0.4 and 0.9 pg As kg per day (ATSDR 2000). 

Although aflatoxin has been shown to be toxic to humans (22), the role of these toxins in human primary liver cancer remains obscure. Epidemiological studies in humans conducted in portions of Africa show a correlation between increased incidence of human primary liver cancer and increase in aflatoxin intake (23). However, epidemiological studies in the U.S. do no indicate a correlation between incidence of primary human liver cancer and aflatoxin consumption. In the Southeast, the average intake of aflatoxin is estimated to be nine times greater than the national average (24). However, according to unpublished data from the... 

Chronic-Duration Exposure and Cancer. Epidemiological studies in humans following chronic exposure to MBOCA are very limited. No information is available regarding toxic effects in humans following chronic exposure to MBOCA. 

As mentioned above, in order to protect the health of consumers, few countries permit the use of chloramphenicol in food-producing animals. In addition to epidemiological studies in humans showing that treatment with chloramphenicol is associated with the induction of aplastic anemia, chloramphenicol is a genotoxin in vivo and may cause adverse effects in humans (discussed further in Chapter... 

Information that is used in the safety assessment of substances for human use includes a knowledge of the chemistry of the substance, the results of studies in experimental animals, and evidence from epidemiological studies in humans. In Chapter 4 of this book it is made evident that LEAR oil is similar in its fatty acid composition to numerous other vegetable oils that are commonly consumed by humans. From this standpoint it is apparent that LEAR oil as normally consumed is, like other vegetable oils, a safe substance for humans. 

In the last several decades, there have been several studies in experimental animals, case reports in humans, case studies in humans, and epidemiological studies in humans on the effects of solvents on the kidney, both acutely and chronically. The scope of diis chapter is the clinical chronic effects of solvents on the kidney (chronic nephrotoxicology). 

Epidemiological Studies in Human Cancer. A number of epidemiological studies have demonstrated some relationship between patterns of dietary ascorbate intake in large population groups and their incidence of cancer of various types and cancer in general (27, 31,70, 86, 107, 143, 144, 149, 154, 158, 180, 353). We propose to review these and similar studies elsewhere. 

Epidemiological studies in humans have so far not shown any embryo-toxicity of cadmium. Traces of cadmium have been detected in aborted human material. In contrast to mercury and lead the concentrations of cadmium in human placentae are very high. This is demonstrated by Fig. 8, which was taken from a publication of Roels and coworkers (1978). These data show that the concentration of cadmium in the human placenta is nearly 10-times higher than cadmium concentrations in maternal and fetal blood. In further determinations cadmium concentrations in mother s milk were considerably lower than maternal blood levels. 

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