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The chemical industry, worldwide. has expanded enormously in quantity of output since the beginning of the last century. The variety of its products has increased considerably since the end of the Second World War.
Worldwide, the industry generates turnover of $1,000 billion every year. In addition to this enormous turnover, it regularly shifts product emphasis, accelerating the production and variety of some types of chemicals and shedding others. The industry focused on paints, agro-chemicals, pharmaceuticals, and high-value plastics as the growth areas of the 1990’s. Many products in the chemical industry are not sold in the general retail market; they are sold on to some other chemical industry for use as a component in the products of the buyer industry. Highest demand for inorganic products of this kind is seen for chlorine, sodium hydroxide, caustic soda, titanium dioxide and hydrogen peroxide.
Chemicals represent Ireland’s third largest export product after machinery and food. Upwards of 12,00 people are employed in Ireland’s chemical industry and the industry and workforce is growing. There are about 200 chemical and pharmaceutical firms in the country. Between 1972 and 1986 turnover in the Irish chemical industry jumped from £36 million to £1,251 million, an increase of 35 fold. Generally, pharmaceuticals and “fine chemicals” are the principal products of the Irish chemical industry. Fine chemicals are required in small volumes and attract high prices, having undergone relatively sophisticated manufacturing techniques. Chemical factories of fine chemicals and pharmaceuticals are large purchasers of bulk chemicals from other chemical manufacturers. In 1986 £165 million of organic chemicals were imported into Ireland for use in the Irish chemical industry.
Needless to say, Ireland is a user of chemicals as well as a manufacturer. Paints, glues, resins, dyes and paper-making all use chemical components in their manufacture and are in general use in Irish industry, not to speak of the fertilizers, pesticides, herbicides and animal health products used in agriculture.
About 5 million chemicals are in common use. In the United States of America, a list of 60,000 substances has been compiled under the Toxic Substances Control Act and the US National Institute of Occupational Safety and Health has produced a list of over 39,000 chemicals in it’s Registry of Toxic Effects of Chemical Substances.
There are reasons to think that such lists represent a fraction of the hazardous chemical substances in circulation. It has been estimated that a new potentially harmful chemical enters industrial use every twenty minutes. This presents a serious problem in the dissemination of information on the hazards presented by these products to the end users or even the workers employed in their manufacture. Equally difficult is the question as to what those hazards are. The sources of information, although substantial as a database, are not complete. A U.S. National Research Council study completed in the early 1980’s found there was no toxicology information on 38% of pesticides, 56% of cosmetics ingredients, 46% of food additives and 78% of industrial chemicals.
Categorisations of hazard are also a problem. Some are based on chemical classification, such as Organic and Inorganic.
Others refer to the material state of the substances e.g. gas, solid, liquid or aerosol etc. A further classification refers to their practical uses e.g. “solvents” will include chemically differentiated substances such as ketones, alcohols, ethers etc.
As an alternative, hazards may be classified on the basis of their effect on the human organism, or the mechanism of toxicity in the human body; e.g. “Reactants” and Non-reactants” are so divided on the test of whether the substance suffers a chemical transformation in the body or not. Substances may be classified as neurotixic, hepatoxic, nephrotoxic, or cardiotoxic etc., referring to the toxic effects produced.
A significant difficulty arises in the case of events of chronic toxicity as opposed to events of acute toxicity. It is a principle of toxicity that there is a quantity threshold for every substance below which no toxic results will occur. The exception is a carcinogenic substance, in view of the evidence that a quantity as small as a molecule of some carcinogenic substances will initiate a cancer.
Threshold Limit Values
The American Conference of Governmental Industrial Hygienists (ACGIH) established a system for determining maximum levels of certain selected substances to which workers might be exposed, without, so far as current knowledge indicated, resulting in an injury to the worker. By implication, the selected substances were all known to cause injury at some level of exposure. In short, the purpose of the exercise was to enable the continuation of the processes in which the exposures took place without, if possible, injuring the workers. It is a fact that many toxic substances are apparently harmless to human beings at very low levels of exposure; some, indeed, are required as trace elements to enable the body’s biochemistry to properly function.
The level at which the ACGIH fixed exposure for any particular substance was called “the Threshold Limit Value.” It was defined as “the level to which it is believed that nearly all workers may be repeatedly exposed day after day without adverse effect”. Each worker’s exposure was taken to be eight hours a day over a forty hour week. In addition the TLV level was taken to be an average for a day’s exposure. Thus, exposure could exceed the TLV in the morning if the afternoon exposure was correspondingly reduced. This was not the case with all substances; some were so potent and dangerous that the TLV was not to be exceeded at all. In such cases the TLV’s were “ceiling values”.
In due course, with the establishment of the Occupational Safety and Health Administration (OSHA) and the National Institute of Occupational Safety and Health (NIOSH) in the U.S. and the Health and Safety Executive in the U.K., the ACGIH system was adopted by these official regulatory agencies and are now official parameters. They are referred to as “exposure limits ” by the U.S. and U.K. agencies but further sub-divided by the Health and Safety Executive into “recommended limits ” and “control limits “.
Since the fixing of the original TLV’s by the ACGIH many of the limits have been found to be too generous. This was always understood by the ACGIH; they stated,
“a small percentage of workers may experience discomfort from some substances at concentrations at or below the threshold limit, a smaller percentage may be affected more seriously by aggravation of a pre-existing condition or by development of an occupational illness”.
Unfortunately, these “small percentages” were larger than first estimated and the current OSHA and the Health and Safety Executive limits show, in many cases, considerable reductions on the original TLV’s.
This should not have come as a surprise. Generally, the basis for the fixing of all such limits was and is the perceived effects of measured doses to laboratory animals, mainly rats and mice. Some knowledge of injury to humans was also available and some limits were fixed for some substances because of their close chemical affinity to other substances of which more was known. There are further difficulties.
For events of acute toxicity (immediate acute poisoning) the fixing of the Threshold Limit Value (TLV) is not a large problem. However, the effect of exposure to a low concentration over a long term is frequently different to brief exposure to a high concentration. It is certainly the case that some substances cause allergies at lower concentrations than their TLV. The TLV refers to toxic effects not allergic effects. While the effect of accumulation of heavy metals in the body is reasonably well known, this is not the case for every toxic substance. In addition, the typical features of acute poisoning may not be present in a case of chronic poisoning from the same substance.
Apart from direct and often difficult-to-detect-effects, it has also been ascertained that chronic poisoning may exert a burden on the body’s homeostatic mechanism and precipitate illnesses not directly attributable to the toxic substance. This has been seen in the case of organic compounds of chlorine and phosphorous, carbon disulfide, hydrocarbons, hydrogen sulfide, amino compounds and heavy metals.
Depending on the substance and the quantity involved, the effect of a toxic substance is not identical in the case of every person. Some people can adapt, or in extreme terms, survive, while others fall ill or die. Some people are vulnerable to injury, such as an allergy, while others are not.