6.4 Thermal contamination

Thermal contamination of environment is connected with working of heat power aggregates and technological heat exchange arrangements. The equipment of thermal power stations, various thermal engines, including motors concern to the first group. In these aggregates heat transforms into mechanical or electrical energy. The second group includes various heating, drying, melting, evaporation, sintering of various materials during their technological processing. Here are also devices for heating of dwellings and other objects.

6.5. Nitrates in foodstuffs and their influence on the human's organism

Nitrates are saline of nitrogen acid the must widespread substance in nature. Nitrates take place in ground, water; they are the chemical component of plants, products of substances exchange in organism of humans and animals. People experience influence of nitrates during living all the time. However, in case when loading of these substances on an organism is too heavy they can have a negative effect.

Nitrates loading on the organism of the person has noticeably increased recently. This problem has arisen due to chemicalixation of the agriculture, application of mineral fertilizers containing nitrogen (potassium niter KNO3, natrium niter NaNO3, ammoniac niter NH4NO3) for increasing agricultural harvest.

The problem of nitrates has two aspects, which are interconnected but have some features. It is the aspect of nitrates in potable water and aspect of nitrates containing in foodstuffs.

Such important components as protein, fat, carbohydrate, vitamins and other, and also various chemical substances: pesticides, toxic elements, nitrates and other take place in foodstuffs. Contents of chemical substances in food can vary in wide range: from the concentration safe for people, to the level which represent actual danger for health. Nitrates serve as the obligatory part of foodstuffs, but their amount should stay in acceptable limits.

There are known over 20 factors able to increase nitrates accumulation in vegetative food. They concern to: light deficit, heat and cold in plants vegetation period, drought and constant overly moistening, large and small amount of such elements as nitrogen, potassium, phosphorum in a ground, biological activity of a ground, ground acidity, ground disease etc. But the primary factor stays non-rational applying of nitrogen fertilizers, violation of agrotechnic processing agricultural cultures.

Intoxication by nitrates is characterized by heavy passing and can cause death. Nitrates toxic action consists in hypoxia (oxygen starvation of tissues). Clinical indications of nitrates poisoning occur in l -l,5 hours after getting into an organism with potable water. At first period there's cyanosis of lips, mucous envelopes, nails, face observed. Then irritating affecting of mucous envelope is exhibited with sickness, pain in stomach area, salivary emissions, vomiting. In case when nitrates get into organism with food the latent period of disease is more prolonged - from 4 till 6 hours.

When there's suspicion of poisoning by nitrates and nitrites patient gets stomach washing out, later, on he takes activated carbon suspension (2 spoons per glass of water), and after that salt laxative mixture.

The hygienic regulation of acceptable concentration for nitrates in separate foodstuffs is carried out with account of concrete climatic and economic regions. Here it is necessary to take into account the acceptable daily doze of nitrates, daily using of food, background nitrates' level in foodstuffs. The acceptable daily doze of nitrates for the person makes 5 mg for 1 kg of body weight.

Nitrates can be accumulated in increased amount not only in vegetative food, but also in food of animal origin and first of all in milk.

As the practice testifies, contents of nitrates in vegetative food quite often exceed acceptable level. That forms the basis for determination of ways for their correct use. The amount of nitrates in plants depends on their biological features. Vegetables contain the most quantity of nitrates in greens (parsley, dill, salad etc), edible roots (garden radish, beet, carrots). Nitrates contents accumulated in tomatoes and potatoes are comparatively slight. Cucumbers and cabbage take place between these two vegetable groups. The early vegetables contain nitrates more, than the latter ones. As the matter of fact nitrates, concentration in hothouse vegetables is more than in vegetables growing in open ground. Rather little nitrates quantity is accumulated in fruit and berries. The researches show, that contents of nitrates in vegetables is distributed irregularly. For example, amount of nitrates in leaves of parsley, fennel is for 50..60 % lower than in their stalks; amount of nitrates in upper part of carrot is for 80% lower than in internal. In cucumbers, radish, on the contrary, the surface layer contains for 70 % of nitrates more than internal.

Usual washing and mechanical clearing of food (potatoes, beet, carrot, cabbage etc) reduces contents of nitrates in average for 10 %. Significant reduction of nitrates is observed on steeping of the cleared food. After steeping of potatoes, carrot, beet during 1 hour the level of nitrates decreases for 25-30%, greens (parsley, fennel, green onions) - for 20 %. The reduction of nitrates contents in food can be reached by cooking. While boiling they turn into broth, what decreases nitrates contents: in potatoes - for 80 %, carrots and cabbage - for 60-70 %, beet - for 40-50 %. Preserving decreases contents of nitrates in food. It is achieved by transition of nitrates into pickle (on souring) or marinade (on pickling and preserving). Making juices and drying of vegetables, on the contrary, increases contents of nitrates.

The important element of maintenance of the guaranteed quality for foodstuffs is controlling them, including parameters of nitrates contents and others chemical polluters in foodstuffs.

Table 3.1 indicates acceptable levels of nitrates contents in some vegetables. j

The controlling of foodstuffs quality is carried out by:

-manufacturer;

• special official establishments - sanitary-epidemic stations;

• public organizations.

For detection of nitrates: there is whole arsenal a research tests:

• photometric methods are based on transformation of nitrates into nitrites with following synthesis of dyes (solution coloring) with nitrites. The intensive the coloring of a researched solution is the more concentration of nitrates is in it;

• chromographic methods: method of gas chromographing, gas-liquid and ionic chromographing. Last is the most perspective for arbitration researches which require high fidelity;

- electrochemical, volt-ampere-meter, potentiometer with application of ion-selective electrodes methods for nitrates дdetection.

Table 1 - Acceptable levels of nitrates contents in some vegetables

Vegetable	Acceptable levels of nitrates contents in foodstuffs, mg/kg
	Open ground	Protected ground
Eggplants	300	-
Beet	1400	-
Melon	90	-
Squash	400	-
Water-melons	60	-
Cabbage late	400	-
Cabbage early	800	-
Potatoes late	120	-
Potatoes early	240	-
Carrots late	300	-
Carrots early	600	-
Vegetables leaves and salad	1500	3000
Cucumbers	200	400
Pepper	200	-
Garden radish	1200	-
Tomatoes	100	200
Onions	400	800
Large onions	90	-

Planning foodstuffs quality tests on parameters of chemical danger the following classification of normal controlling is used:

• once for one year;

• once for one quarter;

• once for one month;

• once for ten days;

• in each foodstuffs lot.