Toxic Chemicals

1.0 INTRODUCTION:
The number of chemicals used in industry is very large and grows each year. Most of the chemicals available in the market are dangerous in one way or other and therefore it needs more attention to understand their potential hazards and control measures. Lack of awareness on these substances has caused many major accidents and some of them even have resulted in catastrophes like Bhopal, Mexico, Seveso, Chernobyl, etc.

The hazards encountered by the industry can be classified as: (i) physical hazard, (ii) mechanical hazard, (iii) chemical hazard, (iv) biological hazard, (v) radiation hazard, (vi) electrical hazard, (vii) fire and explosion hazard, etc. Among these, chemical hazard need more attention because it involves thousands of hazardous chemicals, which not only pose danger to the health of workers but also to the community itself.

According to the nature of hazards, chemicals can be broadly classified as: (i) combustibles, (ii) flammables, (iii) explosives, (iv) substances react with air and/or water, (v) oxidising agents, (vi) radioactive substances, (vii) toxic substances and (viii) corrosives. However, this article is confined to Toxic Substances only.

2.0 TOXIC SUBSTANCES:
Toxic substances are substances, which may cause harmful effect by absorption into the body by (i) inhalation of dust, vapour or mist of the substance; (ii) ingestion of the substance or its vapour or mist and (iii) absorption of the substance through skin and eye. If they are inhaled or ingested or if they penetrate the skin, may involve serious, acute or chronic health risks and even death. Some of the toxic substances are also potential fire hazard and may act in two ways, i.e. first, the high toxicity of certain chemicals themselves may be hazardous in a fire and second, their presence within the fire zone may effectively restrict firefighting operations.
As per its harmful effect on human body, the toxic chemicals can be grouped into the following:

• Chemical Asphyxiants
• Irritants
• Narcotics
• Systemic Poisons
• Carcinogens
• Teratogens
• Mutagens
• Dermatological effects.

Due to limitation of space, only a brief description of the above groups are given below:

2.1 Chemical Asphyxiants:
Chemical asphyxiants are those chemicals, which produces suffocation from lack of oxygen, e.g.: Acrylonitrile and its derivatives, Aniline, Carbon Dioxide, Carbon Monoxide, Nitrogen Gas, Hydrogen Cyanide, Hydrogen Sulphide, Methane, Nitrobenzene, etc.

2.2 Irritants:
An Irritant is a material that will readily migrate, usually through volatilization, to other parts of the body from that part to which it was exposed. These chemicals, mainly enter the body through the respiratory system, and depending on their solubility, they would affect the different parts of the system. Though these substances are non-corrosive, its prolonged or repeated contact with the skin or mucous membrane, can cause inflammation. Some of the irritants that affect the upper respiratory tract are: Acetic Acid, Ammonia, Cynuric Chloride, Formaldehyde, Nitrochlorobenzene, Sulphur Dioxide, etc.
Some of the irritants that affect the pulmonary functions are: Chlorine, Nickel Carbonyl, Nitrous Oxide, Phosgene, etc.
It may be noted here that some of the pulmonary irritants are odourless and have a very low solubility, and therefore, they cause a late reaction but they are very severe.

2.3 Narcotics:
Narcotic is a condition producing stupor or sleep. Narcotics and Anaesthetics have a direct effect on the nervous system including the respiratory centre. The excessive intake of narcotics and anaesthetics causes depression and eventual failure of respiration. In milder exposures, the symptoms would be dizziness, delirium, stupor, coma and convulsions. Some of the chemicals that produce narcotic and anaesthetic effects are: Aniline, Benzene, Carbon Disulphide, Carbon Tetrachloride, Chloroform, Ether, Nitrobenzene, Nitrous Oxide, etc.

2.4 Systemic Poisons:
Systemic means spread throughout the body. Thus, systemic poisons are those substances, which spread throughout the body. Example, several Metal Oxides

2.5 Carcinogens:
A carcinogen is a substance, which can cause cancer. Carcinogenic substances, if they are inhaled or ingested or if they penetrate the skin, may induce cancer in man or increase its incidents. American Conference of Governmental Industrial Hygienists (ACGIH) and the International Agency for Research on Cancer (IARC) has identified a number of materials as carcinogens. The list of carcinogens prepared by these organisations include known human carcinogens and some materials, which cause cancer in animal experiments.

The substance carcinogenic to human include: 4-Aminobiphenyl, Arsenic and its compounds, Asbestos, Benzene, Benzidine, Beryllium, Cadmium and its compounds, Coal-Tar, Chromium Compounds, Ethylene Oxide, Pitches, 2-Naphthylamine, Nickel Compounds, Tobacco, Vinyl Chloride, etc.

Certain chemicals are listed as probable carcinogens to humans which include: Acrylonitrile, Cadmium, Creosotes, Diethyl Sulphate, Dimethylcarbamyl Chloride, Dimethyl Sulphate, Epichlorohydrin, Ethylene Dibromide, Ethylene Oxide, Formaldehyde, Polychlorinated Biphenyls, Silica Crystalline, Styrene Oxide, Tetrachloroethylene, Trichloroethylene, Vinyl Bromide, Vinyl Fluoride, etc.

The substances possibly carcinogenic to human include: Acetaldehyde, Acetamide, Acrylamide, Antimony Trioxide, Bromodichloromethane, Carbon Black Extract, Carbon Tetrachloride, Chlorinated Biphenyls, Cobalt and its Compounds, etc.

2.6 Teratogens:
A Teratogen is a substance, which can cause birth defects. Examples of teratogens are Alcohol, Cocaine, Lead, Mercury Salts, Tetracycline, Tobacco, Warfarin, etc.

2.7 Mutagens:
A Mutagen is a substance, which can cause change in the DNA of the cells. Mutagenic substances, when inhaled or absorbed through the skin or ingested, may lead to heritable or non-heritable genetic damage. Examples of mutagens are: Bromine, Sodium Azide, Psoralen, Benzene, X-Rays, Gamma Rays, Alpha Particles, Ultraviolet Radiation, Etc.

2.8 Dermatological effects:
Dermatology means the study of skin diseases. Dermatitis means inflammation of the skin. The terms ‘dermatitis’ and ‘eczema’ are interchangeable and refer to a particular type of inflammatory reaction of the skin, which may be triggered by internal or external factors. Occupational contact dermatitis is an exogenous eczema caused by the interaction of the skin with a chemical, biological or physical agent found in the work environment.

3.0 CRITERIA FOR TOXIC CHEMICALS:
The criteria for toxic substances vary from agency to agency and also depends upon the route of entry of the substance into the body. Depending upon the toxicity of the chemicals, the chemicals can be classified into various categories.

The criteria for the Classifications of toxic chemicals are based on its toxicity, which is measured as LD 50 and LC 50.

LD 50 stands for Lethal Dose 50. LD 50 is the amount of material, given all at once, which causes the death of 50 percent (one half) of a group of test animals such as rat, mouse, rabbit, dog, monkey, etc. The LD 50 can be determined for any route of entry, but dermal (apply to skin) and oral (given by mouth) are most common. The LD 50 is one measure of the short term poisoning potential of a material.

LC 50 stands for Lethal Concentration 50. LC 50 is the concentration of the materials in air, which causes the death of 50 percent (one half) of a group of test animals such as rat, mouse, rabbit, dog, monkey, etc. The material is inhaled over a set period of time, usually 1 to 4 hours. The LC 50 helps to determine a short term poisoning potential of a material.

The criteria laid down under various statutes in India are outlined below:
3.1 MSIHC Rules:
The Manufacture, Storage and Import of Hazardous Chemical Rules (MSIHC), 1989, framed under the Environment (Protection) Act, 1986, of India, lists 429 hazardous and toxic chemicals under Schedule 1, Part 2 and Threshold Quantity for 179 hazardous chemicals under Schedule 3, Part 1 of the Rule. However, the list of “hazardous and toxic chemicals” have been revised in 2000 amendment of the Rule, which now lists 684 chemicals under “hazardous chemicals”. The MSIHC (Amendment) Rules, 2000, classify toxic chemicals into three categories viz.: (1) Extremely Toxic, (2) Highly Toxic and (3) Toxic and LD 50 and LC 50 values prescribed are shown in Table 1.

3.2 Factories Act:
Section 41–F of the Factories Act, 1948, has prescribed “permissible limits of exposure” of chemical and toxic substances. The maximum permissible threshold limits of exposure of chemicals and toxic substances in manufacturing process (whether hazardous or otherwise) in any factory shall be of the value indicated in the Second Schedule of the Act. The Second Schedule in the Act lists Threshold Limit Values (TLVs) of 125 substances out of which 116 are chemicals. TLV is the occupational exposure limit established by the American Conference of Governmental Industrial Hygienists (ACGIH). TLV is a registered trademark of ACGIH. TLVs are adopted by some Governments including India as their legal limits.

The TLVs, which are also termed as Time Weighted Average concentration (TWA), which means that if the actually measured values in the work places, do not exceed these TWA values, it can be taken for granted that even after repeated exposures to such average concentrations during 8 hours of shift for 5 days a week and throughout the span of work life, the health of only a minimum number of workers will be adversely affected. The actual value is computed by adding the products of each sampling interval and the corresponding concentration, and dividing the sum total by the sum of all the sampling intervals, i.e.

TWA = C1T1 + C2T2 + – – – + CnTn / T1 + T2 + – – – + Tn , where C= Concentration (airborne) and T=Time over which measurement took place (sampling interval).
It is observed that occasional excursions over the TLV cannot be avoided in actual situations. Realising this, the Act has permitted for such excursions during the shift in respect of a few substances. The exposure limits during such excursions (Short Term Exposure Limit or STEL) have been prescribed for 39 substances. STEL is the acceptable exposure limit to a toxic or an irritant substance over a short period of time (TWA), usually 15 minutes. STEL is the maximum concentration of a chemical to which workers may be exposed continuously for a short period of time without any danger to health, safety or work efficiency. This term is used in occupational health, industrial hygiene and toxicology. It may be noted here that the number of times the concentration reaches the STEL should not be more than four (4) and the duration between the two (2) such occurrences should not be more than 60 minutes.

3.3 Motor Vehicles Rules:
The Central Motor Vehicles Rules, 1989, of India has laid down certain criteria for classification of chemicals. As per the Rule, hazardous chemicals are classified into 3 categories, viz. (1) Toxic Chemicals, (2) Flammable Chemicals and (3) Explosives. According to the rule, the toxic chemicals are the chemicals having prescribed values of toxicity (See Table 2) and which, owing to the physical and chemical properties, are capable of producing major accident hazards. However, the Central Motor Vehicles Rules, 1989 has been amended in 2015.

3.4 Insecticides Rules:
As per the Insecticides Rules, 1971, of India, the insecticides are classified into 4 categories, viz. (1) Extremely Toxic, (2) High Toxic, (3) Moderately Toxic and (4) Slightly Toxic. The categories are determined by the toxicity value of the insecticides (LD 50)
and the criteria laid down are given in Table 3

4.0 TOXICITY OF CHEMICALS:
Almost all the chemicals in the market are in one way or other affect ‘Flora and Fauna’. The degree of severity depends upon the nature of chemicals, the duration of exposure and the safe procedures adopted for handling toxic chemicals. Some of the toxic substances, which causes diseases or affect various parts of human body after a prolonged exposure are briefed below:

4.1 Occupational Lung Disease:
Occupational lung diseases are most common amongst the workers who are exposed to various chemicals. Prolonged exposure to Crystalline Silica can cause Silicosis. Exposure to Asbestos can cause Asbestosis, Lung Cancer, Mesothelioma. Coal Workers’ Pneumoconiosis is associated with the exposure of Coal Dust. Beryllium can cause Berylliosis. Exposure to cotton, raw flax, hemp or jute dust can cause Byssinosis. Occupational Asthma can cause due to prolonged exposure of metallic salts like Platinum, Nickel, Chromium, Cobalt, Vanadium, and Tungsten Carbide. Some antibiotics and proteins also induce Occupational Asthma. Hypersensitivity Pneumonitis can result due to the exposure of dust of grain, moldy hay, sugar cane, Toluene Diisocyanate and Copper Sulphate. Asphyxiation, Irritation, Pulmonary Oedema can result due to the exposure of nitrogen, CO2, CO, Methane, H2S, NH3, SO2, Phosgene, and Ozone. Exposure to Arsenic, Asbestos, Chromium, Radium, Nickel, Coke Oven Emissions, can lead to Lung Cancer. Various bacteria, viruses can cause Anthrax, Brucellosis.
Incidentally, many cases of incidence of Silicosis, Asbestosis, Coal Workers’ Pneumoconiosis, Byssinosis, Hypersensitivity Pneumonitis, Lung Cancer, Anthrax, etc. are reported in India, which are recognised as a compensable disease under various statutes in particular, the Factories Act.

4.2 Cardiovascular Toxins:
Toxic agents like Arsenic, Chlorofluorocarbon Propellants, hydrocarbon solvents in particular, 1,1,1 – Trichloroethane, and Trichloroethylene, Organophosphate and Carbonate Insecticides can cause Cardiac Arrhythmia. Exposure to Carbon Disulphide, Carbon Monoxide and Lead, can cause Coronary Artery Disease. Exposure to Cadmium, Carbon Disulphide and Lead may result in Hypertension. Myocardium Injury may cause due to prolonged exposure of Antimony, Arsenic, Cobalt and Lead. Exposure to organic nitrates, e.g. Nitro-Glycerine and Ethylene-Glycol Dinitrate may lead to Ischemic Heart Diseases. Peripheral Arterial Occlusive Disease can occur due to exposure of Arsenic and Lead.

4.3 Liver Toxins:
Cirrhosis, Hepatocellular Carcinoma and Angiosarcoma are most common amongst the pesticide workers handling arsenic. Use of Dioxin is a potential threat to pesticide workers which can lead to Porphyria Cutanea Tarda. Ceramic workers handling Beryllium are likely to affect Granulomatous Disease. Workers involved in dry cleaning can affect Acute Hepatocellular Injury or Cirrhosis due to the use of Carbon Tetrachloride. Acute Hepatocellular Injury can also be caused for – painters using paints containing 2-Nitropropane; munitions workers handling Phosphorous or Trinitrotoluene; workers involved in cleaning by using solvents containing Trichloroethylene. Angiosarcoma is most common amongst rubber workers who use Vinyl Chloride.

4.4 Digestive System Toxins:
Handling of Lead and Mercury for a prolonged period can result in Gingivitis, Glossitis and Stomatitis. Gastritis is a common disease found amongst the workers handling Carbon and its Salts, Carbon disulphide, Chloronaphthalenes and Chromium and its Compounds. Abdominal Pain is very common amongst the workers involved in handling Arsine, Lead, Phosphine, and Bromochloromethane. Prolonged exposure to Lead, Mercury and Pesticides can result in Diarrhoea / Constipation.

4.5 Renal Toxins:
Significant exposure to metals such as Chromium; Cadmium; Mercury; Vanadium; Organic Solvents -Halogenated Hydrocarbons (Carbon Tetrachloride, Ethylene Dichloride, Chloroform, Trichloroethylene, Trichloroethane, Ethylene Chlorohydrin, Vinylidene Chloride); Non-Halogenated Hydrocarbons (Dioxane, Toluene, Methyl Cellosolve, Butyl Cellosolve, Phenol, Pentachlorophenol, Dinitrophenols); Pesticides such as Carbaryl, Arsine and Yellow Phosphorus can contribute to Acute Renal Dysfunction. Prolonged exposure to Lead, Mercury, Uranium, Carbon Disulphide, Beryllium and Organic Solvents can results in Chronic Renal Dysfunction. Exposure to Coke-Oven emissions can lead to Renal Tumour. Bladder Tumour can result in the prolonged exposure of Aromatic Amines such as Benzidine, B-Naphthylamine, 4-Nitrobiphenyl, 4-Aminobiphenyl.

4.6 Reproductive Disorders:
Prolonged exposure of many toxic chemicals, without adequate protection, may result in Reproductive Disorders. Amongst them Lead and Mercury are proven toxic agents, contributing to Menstrual Disorders, Infertility and Spontaneous Abortion. Lead, Mercury, Organic Solvents, Styrene, Ionizing Radiation and DDT are probable toxic agents, which can contribute Congenital Malformations. Lead is a proven toxic agent for Stillbirth. Sperm-Related Disorders are attributed to toxic agents like Carbon Disulphide, Lead, Dibromochloropropane and Methyl Cellosolve.

4.7 Skin Disorders:
Some chemicals when in contact with the skin produce Dermatological Effect for e.g. Acetic Acid, Acrylic Monomers, Cutting Oils, Detergents, Disinfectants, Epoxy Resins, Formaldehydes, Petroleum Distillates, Soap, Solvents, Turpentine, etc. Electronic workers, aircraft assembly workers, construction workers, electric utility workers and painters are prone to Contact Dermatitis due to prolonged exposure to various Epoxy Resins. Prolonged handling of Paraphenylenediamine and related Dyes, without proper protection, can result in Contact Dermatitis in hairdressers and rubber workers. Acrylic Monomers is a potential Health Hazard to dental technicians, printers, and acrylic ink manufacturers, who handle these chemicals without adequate protection. Metals like chromium, Nickel, Cobalt and Platinum can contribute Contact Dermatitis, which can be affected by cement workers, hairdressers and electronic assemblers. Pharmaceuticals like Chlorpromazine, Glutaraldehyde, Penicillin, and Neomycin can affect the health of veterinarians, health care workers and pharmacists, if they handle these chemicals without adequate protection. Outdoor workers like farmers, fishermen, sailors, etc., can get Skin Disorders from the exposure of Cutaneous Carcinogens like Ultraviolet Lights (256 to 320 nm). Radiologists, X-Ray technicians, uranium miners and refiners are prone to Ionizing Radiations like X-Rays, Gamma Rays, Beta Rays, Gamma Particles, Protons and Neutrons. Gold miners and chemical workers exposed to Inorganic Arsenic can get various Skin Disorders.

4.8 Haematological Disorders:
Toxic chemicals like Aniline, Nitroanilne, P-Chloroaniline, Toluidine, O-Toluidine, Naphtaline, Paradichlorobenzene, Nitrates and Trinitrotoluene are associated with Methaemoglobinaemia and if appropriate precautions are not taken, the workers involved in handling these chemicals, can get Haematological Disorders. The chemicals like Arsenic, Benzene, Trinitrotoluene, Pentachlorophenol, Hexachlorocyclohexane, Ethylene Glycomonomethyl or Monobutyl Ether and DDT are associated with Aplastic Anaemia. The workers involved in the manufacture of synthesis of fabrics, pesticides, rubber, solvents for varnishes, glues, paints, inks, enamels, tanning agents, dyes and cleaning agents can get Haematological Disorders.

5.0 CONCLUSION:
The very purpose of identification and classification of chemicals, in particular toxic chemicals, is to fulfil the need for conveying information on protection against hazard to the user in the most direct manner. The criteria for the toxic substances vary from agency to agency and also depends upon the route of entry of the substance into the body. The degree of severity depends upon the nature of chemicals, the duration of exposure and the safe procedures adopted for handling toxic chemicals. Establishment of a structure for harmonising classification and values for toxic chemicals would have a beneficial impact on the exchange of information related to chemicals, on the cost of risk assessment and management of chemicals and ultimately on the protection of workers, the general public and the environment. The efforts initiated by various organisations may result in an ideal classification system for toxic chemicals.

6.0 REFERENCES:

1. American Conference of Governmental Industrial Hygienists – Documentation of the threshold limit values and biological exposure indices, Cincinnati, ACGIH.
2. Carl Zenz – Occupational Medicine. Chicago, Year Book Medical Publishers, 1975.
3. Encyclopaedia of Occupational Health and Safety, 4th Ed. (4 Volumes), Geneva, ILO, 1998.
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5. India – The Central Motor Vehicles Rules, 1989 and amendments.
6. India – The Environment (Protection) Act, 1986.
7. India – The Factories Act, 1948 with amendments and Maharashtra Factories Rules, 1963.
8. India – The Insecticides Rules, 1971.
9. India – The Manufacture, Storage and Import of Hazardous Chemicals Rules, 1989.
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21. Nair, R.R. – Hazards of Benzene. (SHS-4) New Bombay, Safety and Health Information Bureau, 1989.
22. Nair, R.R. – Hazards of Carbon Disuphide. (SHS-5) New Bombay, Safety and Health Information Bureau, 1989.
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Article by —–

Mr. R. R. Nair is currently the Director of Safety and Health Information Bureau. He is an ex-employee of Central Labour Institute, DGFASLI, Mumbai, and retired from the Government Service after 28 years. He has more than 50 years’ experience in occupational safety, health & fire protection. He participated in a number of seminars, conferences, workshops on safety, health and fire protection at National and International levels. He has carried out about 85 projects in safety, health, environment and fire protection (safety audits, accident investigations, environmental studies, hazard identification and risk assessment (HIRA), hazardous zone classifications, fire safety audits in high rise buildings, etc.) PAN India. He is author of 15 books and about 80 articles in various topics on safety and allied subjects.

He can be contacted on:
M: +91 7045172050, +91 9224212544
Resi: +91 477 2266994
E-mail: ceo@shib.co.in / shib@vsnl.com
Website: www.shib.co.in