Examples of risk assessment risk evaluation and risk management

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The examples in this section underline the importance of risk assessment, evaluation, and management. Furthermore, they will show the lack of necessary information and its implications for risk assessment and ranking of risks. In fact, these examples explain the ranking order of food hazards as shown in Table 16.2. In each example, the following items will be addressed: toxicity of the substance concerned, its daily intake and the duration of use, the sensitivity of the consumer, and the existence of high-risk groups.

16.3.3.1 Additives and processing residues According to the general public, the toxicological risks associated with the intake of food additives and food processing residues are high. In particular, sweeteners, antioxidants, dyes, and preservatives are substances that have recently received large negative publicity.

In contrast, more objective scientific criteria prove the toxicological risk from additives to be minimal. For most of these substances extensive information on toxicity is available; acute and subacute toxicity as well as chronic toxicity, including mutagenicity, carcinogenicity and teratogenicity, have been investigated. Epidemiological (human) data, however, are scarce.

16.3.3.1.1 Saccharin. Risk assessment — Toxicity. Saccharin is a sweetener which, at very high doses, has been shown to cause bladder tumors in experimental animals. Generally, for components suspected to be carcinogenic, the risk is estimated from so-called "calculated mortality" (see Section 16.3.2), the linear extrapolation to a virtually low risk level. However, the doses at which bladder tumors were shown to develop in experimental animals were very high. The carcinogenicity of saccharin appeared to be due to the formation of bladder stones, rather than to genotoxicty (interaction at DNA-level). Therefore, the use of saccharin has been approved in the U.S. and Europe, and the ADI calculation using the calculated mortality procedure was not applied. For safety reasons, the maximum daily intake was advised to be 2.5 mg/kg body weight. No epidemiological study has shown that cancer incidence and mortality are related to the use of saccharin.

Risk assessment — Intake. In general, the daily intake of saccharin is below the ADI. Soft drinks are allowed to contain a maximum of 200 mg saccharin/kg. The average use of soft drinks is 300 g/day, which means a maximum of 70 mg saccharin/day. However, the daily saccharin intake by diabetic patients may be several times higher than that of non-diabetics.

Risk assessment — Sensitivity. There is no evidence for an increased sensitivity of specific subpopulations. Diabetic patients may be a high-risk group owing to their extensive intake, rather than high sensitivity.

Risk evaluation. Saccharin most probably does not pose an important health risk to humans. It has been calculated that a cancer risk may only develop at a daily saccharin dose present in 800 cans of soft drink (equivalent to the sweetness of 25 kg of sugar). This agrees with the fact that no increased cancer risk for diabetic patients has been observed in epidemiological studies.

Risk management. Saccharin is already the subject of risk management. Its use in foods is regulated by several food acts. Saccharin-containing sugar substitutes should be labeled with the warning not to use more than 80 mg/day. Saccharin is prohibited in baby food. Authorities are also involved in risk management by checking the observation of food regulations and by giving proper dietary advice and information to diabetics. Scientists take part in saccharin risk management, for example, by investigating the need for diabetics to use sugar substitutes.

For most additives the situation is very similar: extensive toxicological information is available, and legislation on use is provided for. To this end, so-called "positive lists" are made up, i.e., an additive not on this list is not allowed to be used unless explicitly stated otherwise by law. In fact, additives are considered to be the safest food components. The toxicological risks from this category are believed to be minimal. However, there are a few examples of additives for which the evaluation of toxicological risks is more difficult. This is mainly due to interactions with other toxic substances, such as contaminants.

16.3.3.1.2 Nitrite (and nitrate). Nitrite is an important preservative. It is used in the production of cheese and meat products. Nitrite inhibits the growth and development of Clostridia bacteria. Exposure to the contaminant nitrate mainly occurs by drinking water and consumption of leafy vegetables.

Risk assessment — Toxicity. Toxic effects of nitrite include methemoglobinemia, leading to disturbances in oxygen supply, and hypertrophy of the adrenal zona glomerulosa.

Nitrite can also react with secondary amines to form N-nitrosamines, which have proved to be carcinogenic in several experimental animals. The toxic effects of nitrate originate from its bacterial reduction to nitrite in the oral cavity. Some epidemiological studies have suggested that in subjects with gastric lesions a higher risk of gastric tumors may be associated with a high nitrate intake. However, such effects have not been observed in non-patients, so that the evidence is limited.

The no-observed-adverse-effect level (NOAEL) of nitrite as calculated from the results of chronic toxicity studies in rats is 10 mg NaNO2 or 6.7 mg NO- per kg body weight. Since there is a difference in the reduction of nitrate to nitrite between rats and humans, the NOAEL of nitrate is calculated from the NOAEL of nitrite. Estimating the conversion of nitrate to nitrite at 5%, the NOAEL for adults is: 100/5 x 10 mg/kg body weight = 200 mg NaNO3 per kg body weight or 146 mg NO- per kg body weight. Currently, the ADI values are 5 mg NaNO3 per kg body weight (3.65 mg NO- per kg body weight) and 0.2 mg NaNO2 per kg body weight (0.13 mg NO- per kg body weight).

Endogenous nitrosamine (dimethyl- and diethylnitrosamine) formation has been demonstrated in human volunteers on a diet rich in fish and nitrate-containing products. Using the conservative one-hit model with linear extrapolation for carcinogenic substances (see Section 16.3.2) the acceptable daily dose for prevention of a lifetime tumor incidence of 10-6 can be calculated. For dimethylnitrosamine, this value amounts to 16-186 x 10 mg/day, and for diethylnitrosamine to 11-14 x 10 mg/day.

Risk assessment — Intake. According to the Dutch Food Act, addition of nitrate to foods other than cheese, melted cheese, and meat products is not allowed. For these products maximum acceptable limits are indicated, e.g., a maximum of 500 mg KNO3 and 200 mg KNO2 per kg meat. For baby foods, a maximum of 50 mg NO- per kg dry matter is allowed. Leafy vegetables such as spinach contain high concentrations of nitrate by nature. Standards given in the Dutch Food Act are a maximum of 3500 mg NO- per kg in summer, and 4500 mg NO- per kg in winter.

A recent survey has shown that the average daily nitrate intake in the Netherlands ranges from 1.25 mg/kg body weight for men aged 65 to more than 3.6 mg/kg body weight for 1 to 3 year olds. These data were arrived at by combining information from a dietary survey in a large representative subpopulation with information on the nitrate content of various food products. Particularly among children, an excessive nitrate intake (higher than ADI) occurred quite frequently (20 to 40%). The intake of nitrite is probably lower than the amount of nitrite formed endogenously, and is estimated at 2.3 mg NO-per day. Water accounted for 4% of the nitrate intake, while leafy vegetables such as spinach accounted for about 45% of the total estimated intake.

Risk assessment — Sensitivity. Infants are more sensitive to nitrite, resulting in nitrite-induced methemoglinemia, often leading to oxygen supply problems. Also in babies, nitrate is more extensively reduced to nitrite.

Risk evaluation and management. The toxicological risk of the preservative nitrite itself is probably low. Its use is regulated, as is the use of other additives like saccharin.

A major cause for concern is the fact that for many people in general and many children in particular the intake of nitrate is larger than the ADI. In the future, more attention should be paid to the reduction of nitrate emission, e.g., in the form of fertilizer, into the environment. This is the concern of the authorities; the agricultural sector in particular is responsible for this. The health effects of high nitrate intake by children as well as the validity of the current ADI levels need to be examined in more detail. The effects of food preparation on the nitrate content and the consumption of leafy vegetables, especially in winter, ask for attention. Public advice concerning this issue should be considered.

16.3.3.2 Environmental contaminants In general, contaminants are believed by the consumer to pose high risks to health. According to the experts, however, environmental contaminants only rank fourth on the list of food hazards, as shown in Table 16.2.

Concerning polychlorinated dibenzo-p-dioxins and biphenyls — the subject of the next example — the public paid much attention to the high levels found in milk from cows grazing in the vicinity of waste incinerators. However, the guide values for contaminants are based on cumulative, life-long exposure. Therefore, the life-long duration of individual exposures should be taken into consideration when estimating the risks from such high levels of contaminants.

16.3.3.2.1 Polychlorinated dibenzo-p-dioxins and biphenyls. Dioxins are emitted by waste incinerators. They are also known as by-products in pesticides. Polychlorinated biphenyls (PCBs) are well-known environmental contaminants, originating from their earlier use in transformers, and more recently in heat insulation.

Risk assessment — Toxicity. As far as the toxicity of dioxins is concerned, the congener 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is known best. Wasting syndrome (weight loss) is a characteristic acute toxic effect of TCDD in animals. TCDD is not mutagenic. It induces to a large extent the biotransformation enzymes in the liver. Therefore, it is assumed to have a tumor-promoting effect. One epidemiological study reported an association between TCDD exposure and cancer occurrence in a group of workers in a chemical industry. In animals, also immunotoxic and teratogenic effects have been observed. Humans which were exposed to TCDD, e.g., as a result of an occupational accident, developed chloracne. Dioxins and PCBs can have similar biological effects. However, they differ in the intensity of their effects. Therefore, the so-called TCDD equivalent (TEQ) was introduced, relating the toxicity of all dioxins and PCBs to that of TCDD.

When rats were submitted to a lifetime exposure of 1000 pg TCDD per kg body weight, the effects in the liver were minimal. This dose was considered to be a "marginal-effect-level" from which the TDI was calculated using a safety factor of 250. Therefore, the Dutch TDI was 4 pg TCDD or TCDD equivalents per kg body weight. Recently, however, the WHO assessed the TDI at 10 pg TEQ per kg body weight. This value was obtained by using a toxicokinetic approach for humans, resulting in a NOAEL of 1000 pg TCDD per kg body weight. A safety factor of 100 was applied to calculate TDI. This TDI is identical to a lifetime maximum of 255.5 ng TEQ per kg body weight for 70 years.

Risk assessment — Intake. The daily exposure of the general population is estimated on the basis of data on the intake of foods by a representative subpopulation in combination with data on the dioxin and PCB contents of foods as determined by chemical analyses. Using this approach, the daily exposure is estimated to be about 130 pg TEQ, i.e., 2 pg TEQ per kg body weight for adults and 7 pg TEQ per kg body weight for infants. More than 95% of this exposure results from the intake of animal fat. Dairy products are estimated to account for 30 to 50% of the total exposure. Recently, life-long exposure was estimated at 70 ng/kg body weight for dioxins and structurally related substances.

Risk assessment — Sensitivity. About 1% of the children younger than 6 years are estimated to have an exposure of more than 10 TEQ per kg body weight per day. In this respect, the dioxin and PCB contents of breast milk are also of importance. Dairy milk has been shown to contain 2 to 4 pg TEQ per g fat. For breast milk, this is about 35 pg/g fat, implying that breast-fed infants are exposed to about 250 pg TEQ per kg body weight.

Risk evaluation and management. The exposure of breast-fed infants is only four times lower than the marginal-effect-level for rats. Therefore, the TEQ of breast milk certainly needs attention. On the other hand, it should be noted that the TDI levels are cumulative values, calculated on the basis of the results of a number of studies. This implies that conclusions are not allowed if, as is the case for breast-fed babies and children, these limits are exceeded during short periods of time. As far as risk evaluation is concerned, it should also be noted that from a nutritional point of view, for small babies breast milk has definite advantages over cow's milk. Therefore, breast-feeding should certainly not be discouraged. Other management measures, such as reduction of dioxin and PCB formation and emission, and checking of foods, are preferred.

Other groups with potentially higher exposures are, for example, industrial workers or individuals consuming milk and cheese from polluted areas near waste incinerators. Industrial safety, and food control should prevent toxic exposure of these groups.

16.3.3.3 Nutritional imbalance As shown in Table 16.1, the consumer does not consider the risks associated with nutritional imbalance to be very important. However, since the beginning of this century it has become clear that the occurrence of several important chronic disorders, such as cardiovascular diseases and cancer, is affected by nutrients which form a substantial part of the diet. Epidemiological studies are particularly useful in bringing these risks to light. As a result, experts generally rate the risk of nutritional imbalance to be one of the highest of all food aspects. Several national nutritional councils have published extensive reports on the macro- and micronutrient contents of foods. For each nutrient, the so-called recommended dietary allowance (RDA) is given, also in relation to high-risk groups such as infants, children, pregnant women, and the elderly. These RDAs guarantee that the intake by 95% of the population is sufficient from a nutritional point of view. In addition, all major nutritional councils have prepared dietary recommendations for overall health maintenance. These guidelines are based on knowledge of the effects of nutrients and foods on the occurrence of chronic diseases, such as cardiovascular diseases and cancer.

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