Friday, May 24, 2013

How Many Chemicals Are There in the World?

According to the Chemical Abstracts Service (CAS), 60 million substances were registered as of May 24, 2011. Counting chemicals is like counting bacteria--it is difficult to get to an end point. Surely, however many chemicals counted, many more can by made by various reactions (e.g., synthesis, decomposition, displacement, or combustion) of already existing chemicals.

According to the Wikipedia article on bacteria, "Following present classification, there are a little less than 9,300 known species of prokaryotes, which includes bacteria and archaea but attempts to estimate the true number of bacterial diversity have ranged from 107 to 109 total species – and even these diverse estimates may be off by many orders of magnitude." From "9300 known" the number drops to several hundred significant bacterial infections as described in Control of Communicable Diseases Manual updated every few years by the World Health Organization.

Chemicals are classified in Haz-Map by "Major Category" and "Category." The twelve major categories are Metals, Solvents, Pesticides, Mineral Dusts, Toxic Gases & Vapors, Plastics & Rubber, Biological Agents, Nitrogen Compounds, Other Classes, Other Uses, Dyes, and Physical/Radiation. The medical informatics problem is similar in both toxicology and bacteriology--the need for a hierarchical classification system that converts data into useful knowledge. Instead of an overwhelming list of 60 million chemicals (many of which are mixtures, alloys, drugs, or rarely used research chemicals) there are 250 classes of chemicals within these 12 major categories to assess in Haz-Map.

It is not necessary to test all 80 million substances for us to have a good understanding of occupational toxicology any more than it is necessary for us to study all billion species of bacteria before we can establish an effective program to prevent infectious diseases. For example, there are now in Haz-Map 336 saturated aliphatic hydrocarbons (single-bonded carbon and hydrogen compounds) with similar adverse effects and 63 lead compounds with similar adverse effects. Do we need to test each aliphatic hydrocarbon and each lead compound? The classification of chemicals (or bacteria) is a way to deal with the complexity of nature so that we can control and prevent diseases and not get lost in the details.

Classification for Prevention:
  1. 250 Categories of Chemicals;
  2. 25 Adverse Effects Caused by Chemicals;
  3. Descriptions of Classes of Chemicals;