Page 258 - Textbook of Pathology, 6th Edition

242 ENVIRONMENTAL CHEMICALS
INJURY BY PHYSICAL AGENTS
A large number of chemicals are found as contaminants in
the ecosystem, food and water supply and find their way THERMAL AND ELECTRICAL INJURY
into the food chain of man. These substances exert their toxic Thermal and electrical burns, fall in body temperature below
effects depending upon their mode of absorption, 35°C (hypothermia) and elevation of body temperature above
distribution, metabolism and excretion. Some of the 41°C (hyperthermia), are all associated with tissue injury.
substances are directly toxic while others cause ill-effects via
their metabolites. Environmental chemicals may have slow Hypothermia may cause focal injury as in frostbite, or
damaging effect or there may be sudden accidental exposure systemic injury and death as occurs on immersion in cold
SECTION I
such as the Bhopal gas tragedy in India due to accidental water for varying time.
leakage of methyl isocyanate (MIC) gas in December 1984. Hyperthermia likewise, may be localised as in cutaneous
Some of the common examples of environmental burns, and systemic as occurs in fevers.
chemicals are given below: Thermal burns depending upon severity are categorised
1. Agriculture chemicals. Modern agriculture thrives on into full thickness (third degree) and partial thickness (first
pesticides, fungicides, herbicides and organic fertilisers and second degree). The most serious complications of burns
which may pose a potential acute poisoning as well as long- are haemoconcentration, infections and contractures on
term hazard. The problem is particularly alarming in healing.
developing countries like India, China and Mexico where Electrical burns may cause damage firstly, by electrical
farmers and their families are unknowingly exposed to these dysfunction of the conduction system of the heart and death
hazardous chemicals during aerial spraying of crops. by ventricular fibrillation, and secondly by heat produced by
Acute poisoning by organophosphate insecticides is quite electrical energy.
well known in India as accidental or suicidal poison by
inhibiting acetyl cholinesterase and sudden death. INJURY BY RADIATION
Chronic human exposure to low level agricultural As discussed in the preceding chapter, the most important
chemicals is implicated in cancer, chronic degenerative form of radiation injury is ionising radiation which has three
diseases, congenital malformations and impotence but the types of effects on cells:
exact cause-and-effect relationship is lacking. i) Somatic effects which cause acute cell killing.
According to the WHO estimates, about 7.5 lakh people
are taken ill every year worldwide with pesticide poisoning, ii) Genetic damage by mutations and therefore, passes
General Pathology and Basic Techniques
half of which occur in the developing countries due to ready genetic defects in the next progeny of cells.
availability and indiscriminate use of hazardous pesticides iii) Malignant transformation of cells (Chapter 8).
which are otherwise banned in advanced countries. Pesticide Ionising radiation is widely employed for diagnostic
residues in food items such as in fruits, vegetables, cereals, purpose as well as for radiotherapy of malignant tumours.
grains, pulses etc is of greatest concern. Radiation-induced cell death is mediated by radiolysis of
water in the cell with generation of toxic hydroxyl radicals
2. Volatile organic solvents. Volatile organic solvents and (page 32). During radiotherapy, some normal cells coming
vapours are used in industry quite commonly and their in the field of radiation are also damaged. In general,
exposure may cause acute toxicity or chronic hazard, often radiation-induced tissue injury predominantly affects
by inhalation than by ingestion. Such substances include endothelial cells of small arteries and arterioles, causing
methanol, chloroform, petrol, kerosene, benzene, ethylene necrosis and ischaemia.
glycol, toluene etc.
Ionising radiation causes damage to the following major
3. Metals. Pollution by occupational exposure to toxic organs:
metals such as mercury, arsenic, cadmium, iron, nickel and 1. Skin: radiation dermatitis, cancer.
aluminium are important hazardous environmental 2. Lungs: interstitial pulmonary fibrosis.
chemicals. 3. Heart: myocardial fibrosis, constrictive pericarditis.
4. Aromatic hydrocarbons. The halogenated aromatic 4. Kidney: radiation nephritis.
hydrocarbons containing polychlorinated biphenyl which are 5. Gastrointestinal tract: strictures of small bowel and
contaminant in several preservatives, herbicides and oesophagus.
antibacterial agents are a chronic health hazard. 6 Gonads: testicular atrophy in males and destruction of
ovaries.
5. Cyanide. Cyanide in the environment is released by 7. Haematopoietic tissue: pancytopenia due to bone marrow
combustion of plastic, silk and is also present in cassava and depression.
the seeds of apricots and wild cherries. Cyanide is a very 8. Eyes: cataract.
toxic chemical and kills by blocking cellular respiration by Besides ionising radiation, other form of harmful
binding to mitochondrial cytochrome oxidase.
radiation is solar (u.v.) radiation which may cause acute skin
6. Environmental dusts. These substances causing injury as sunburns, chronic conditions such as solar keratosis
pneumoconioses are discussed in chapter 17 while those and early onset of cataracts in the eyes. It may, however, be
implicated in cancer are discussed in Chapter 8. mentioned in passing here that electromagnetic radiation