Toxic substances naturally occurring

Assessment of whether a chemical has the potential to cause adverse effects in humans arises usually from direct observation of an effect in animals or humans, such as the acute poisoning episodes that have occurred when potatoes contain high levels of glycoalkaloids. Epidemiological studies have also been used to infer a possible relationship between intake of a particular type of food, or constituent of that food, and the potential to cause an adverse effect. Such observations led to the characterisation of the aflatoxins as human carcinogens. However, natural toxic substances that occur in plant foods have often been identified through observations in animals, particularly farm animals. It was observations of adverse effects in farm animals that led to the further characterisation of the phytoestrogens and the mycotoxins. In other instances, the concern arises from the chemical similarity to other known toxins. 

Acute bioassays are designed to assess the effects of toxic substances that occur within a relatively short period after exposure (48-96 h). The effluent toxicity elicited by test organisms is often fatal and rarely reversible. The relevant information to be gained from this type of test is the distribution of the exposure-response relationship and the nature and potency of the toxic effects, such as immobility, percentage mortality, and time interval to mortality. 

A rigorous approach to studies of naturally produced toxic materials would involve isolation of the compounds in pure form and demonstration that the substances isolated were actually responsible for the observed inhibition. Synthesis and confirmation of activity of the synthetic vs. the natural material may also be required. These criteria have been met in relatively few cases. Unfortunately, studies with naturally occurring inhibitors have been made primarily by plant physiologists without sufficient assistance from chemists. 

Laboratory analysis of site soils should be made to determine the presence and population density of naturally occurring microbes that are capable of degrading the contaminant. At a minimum, these analyses should include plate counts to determine the relative number of microbes of several types, the substrate (food) type that reflects the type of chemicals they are likely to consume, and if toxic substances are present. 

This document deals only with estimating exposure to direct additives and chemical contaminants. The procedures used to estimate exposure to chemical contaminants in food (including naturally occurring toxicants, such as mycotoxins) are essentially the same as those used for direct additives. Thus, contaminants will be considered in the discussion of direct additive exposure estimation. The procedures discussed herein are equally applicable to color additives, GRAS substances, prior-sanctioned ingredients, and pesticide residues. 

Polymerization, or conjugation, is the process in which toxic organic molecules undergo microbially mediated transformation by oxidative coupling reactions. In this case, a contaminant or its intermediate product(s) combines with itself or other organic molecules (e.g., xenobiotic residues, naturally occurring compounds) to form larger molecular polymers that can be incorporated in subsurface humic substances. 

The creatures of the world, both animals and plants, produce a wide range of biologically active substances. Biologically active substances produced by animals or plants that cause an adverse effect are called toxins. Toxins refers only to toxic agents produced by animals and plants, not toxic substances such a lead or pesticides. The classification of a substance as a toxin tends to be in the eye of the beholder. Is caffeine, a naturally occurring agent in many plants, a toxin or just a pharmacologically active compound or both ... 

Biochemical transformations of organic compounds are especially important because many reactions, although thermodynamically feasible, occur extremely slowly due to kinetic limitations. For example, we might be interested in the question of whether benzene can be biodegraded under naturally occurring methanogenic conditions (see Illustrative Example 17.1). Such natural attenuation of this toxic aromatic substance may be thermodynamically allowed under the perceived conditions. But these conditions may not be accurate (e.g., the benzene and methane chemical activities in the system). Also other environmental factors may cause the rate to be unobservably slow. One possibility is that the relevant microorganisms are simply not active in the environment of interest. 

First, it s important to realize that everything, including your own body, is made of chemicals. There is no such thing as a "chemical-free" food, cosmetic, cleanser, or anything else. Second, there is no meaningful distinction between a "natural" substance and a "synthetic" one a chemical is a chemical. Many naturally occurring substances—strychnine, for example—are extraordinarily toxic, and many synthetic substances—polyethylene, for example—are harmless. 

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