Naturally occurring toxicants

LiENER I E (1983) Naturally occurring toxicants in foods and their significance in the human diet. Arch Toxicol Suppl. 6 153-66. 

WHO. 1992. Technical Report Series 828. Evaluation of certain food additives and naturally occurring toxicants. Thirty-ninth report of the Joint FAO/WHO Expert Committee on aTood additives. World Health Organization. Geneva, Switzerland. 

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. 

Rosenthal GA, Bell EA (1979) Naturally occurring toxic nonprotein amino acids. In Rosenthal GA, Janzen DH (eds) Herbivores, their interaction with secondary plant metabolites. Academic Press, New York Witthohn K, Nauman CM (1984) Z Natirrforsch 39 837 Aschoff H-J, Pfeil E (1970) Hoppe-Seyler s Z Physiol Chem 351 818 Jansen 1, Woker R, Kula M-R (1992) Biotechnol Appl Biochem 15 90 Smitskamp-WOms E, Brussee J, van der Gen A, van Scharrenburg GJM, Sloothaak JB (1991) Reel Trav Chim Pays-Bas 110 209... 

Rosenthal, G. A. and Bell, E. A. (1979). Naturally occurring toxic nonprotein amino acids. In Herbivores Their Interaction with Secondary Plant Metabolites, ed. G. A. Rosenthal, and D. H. Janzen, pp. 353-385. New York Academic Press. 

The Joint FAO/WHO Expert Committee on Food Addihves (JECFA) is an international expert scientihc committee that is administered jointly by FAO and WHO. It has been meeting regularly since 1956, inihally to evaluate the safety of food addihves. Its work now also includes the evaluation of contaminants, naturally occurring toxicants, and residues of veterinary drugs in food. These evaluations are collected in a report published after each JECFA meeting (Section 3.6.1.3) (JECFA 2006). 

Toxicological evaluations of food additives and of contaminants, naturally occurring toxicants and residues of veterinary drugs in food produced by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), and of pesticide residues in food by the Joint FAO/WHO Meeting on Pesticide Residues (JMPR) are used by the Codex Alimentarius Commission and national governments to set international food standards and safe levels for protection of the consumer. 

This naturally occurring toxicant is an analogue of acetate and is incorporated into acetyl CoA (fluoroacetate) and hence into Krebs cycle (TCA cycle) as fluorocitrate. This blocks the enzyme aconitase, as the fluorine atom cannot be removed. The TCA cycle is blocked, and citrate accumulates. The mitochondrial energy supply is disrupted, hence cardiac damage occurs. Lack of oxaloacetate will allow ammonia to accumulate leading to convulsions. 

Hartmans, S., Schmuckle, A., Cook, A. M. Leisinger, T. (1986). Methyl chloride naturally occurring toxicant and C-l growth substrate. JoarW of General Microbiology, 132, 1139-42. 

There are numerous kinds of toxicants that may cause alterations in ecosystems. These are normally regarded as pollutants from anthropogenic sources, but they may come from natural sources as well. Examples of such naturally occurring toxicants are hydrogen sulfide from geothermal sources or heavy metals, such as lead, leached from minerals. 

One of the features of areas of the world that have had naturally occurring toxic soils for many thousands or millions of years is that these soils often support species that are found nowhere else so-called edaphic endemics (Kruckeberg and Rabinowitz, 1985). Examples of such soils include the Great Dyke in Zimbabwe and serpentine soils in many areas of the world. It has been argued on many occasions (eg, Proctor and Woodell, 1975 Kruckeberg, 1984) that the phenomenon of metal tolerance provides a model of how these species may have started on the evolutionary route that finally led to full edaphic endemism. 

Table 4.1 Environmental factors affecting the distribution of naturally occurring toxic chemicals in water and soil... 

Geological setting1 Source of water Climate Naturally occurring toxic chemicals that may be found in water Land uses that may Additional chemicals increase concentrations that may be released of possible constituents from natural sources, of water due to land uses given in previous column ... 

We have seen how micro-organisms such as fungi, bacteria, and plankton can cause toxic contamination of food. Plants themselves may also have naturally occurring toxic constituents. For example, as we saw in the discussion on herbal remedies in Chapter 6, the pyrrolizidine alkaloids are found in many plants which may contaminate crops such as wheat and hence find their way into the food we consume. 

Naturally-occurring toxic materials (e.g. mercury and molybdenum compounds)... 

For food additives including flavours, contaminants, and naturally occurring toxicants, the Committee ... 

For contaminants and naturally occurring toxicants, levels corresponding to tolerable intakes such as the provisional maximum tolerable daily intake (PMTDI) or provisional tolerable weekly intake (PTWI) are established when there is an identifiable no-observed-effect level, that is, a threshold of effect can be assumed based on available data. When a noobserved-effect level cannot be identified, the Committee provides other advice, such as identification of the food(s) that contributes most to intake. This allows for targeted management actions in order to decrease exposure. 

WHO, Food Additives Series, 30, Toxicological Evaluation of Certain Food Additives and Naturally Occuring Toxicants, paper presented at 39th Meeting of the Joint FAOAVHO Expert Committee on Food Additives, Geneva, 1993a. 

Conversely, the expression of a yeast derived invertase in potatoes leads to a reduction of these naturally occurring toxicants. The elucidation of the biochemical reason for this reduction (dilution effect due to the increase of the tubers or metabolic interference with the sugar moieties needed for the biosynthesis of the glycoalkaloids) is part of our ongoing research. 

Thus radon presents an interesting case of a naturally occurring toxic material (i.e. a hazard) which has been present in the human environment throughout evolution but which has only recently come to be considered as presenting a risk due to human activities... 

Removal of Naturally Occurring Toxicants through Enzymatic Processing... 

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