The New Straits Times, July 4, 1998
QUESTION: I came across a news report on carbonated drinks in England being tainted with benzene at concentrations above 10ppm. Can you describe the health effects of consuming such products?
ANSWER: Benzene has a long history of extensive use in industry as a volatile solvent and later as a starting material for the synthesis of other chemicals. In Malaysia, the solvent has been said to facilitate the rapid development of the rubber industry because of its ability to dissolve latex and then rapidly evaporate, leaving formed or coated rubber products.
Its other uses include as intermediates in the production of styrene, phenol, cyclohexane, and other organic chemicals as well as in the manufacture of detergents, pesticides, solvents and paint removers.
The immediate toxic effects of acute exposure to high concentrations of benezene of up to 2,000ppm, is depression of the central nervous system. Death occurs in five to 10 minutes. The victim would develop convulsive movements, paralysis and unconsciousness.
Brief exposure to concentrations in excess of 3,000ppm is irritating to the eyes and respiratory tract while continued exposure may cause euphoria, nausea, a staggering gait or movement and coma. Inhalation of lower concentrations (250 to 500ppm) produces vertigo, drowsiness, headache, and nausea.
The most significant toxic effect of benzene exposure is an irreversible injury to the bone marrow. Long-term exposure to low concentrations has been observed to have an initial stimulant effect on the bone marrow, followed by aplasia (defective development of the organ) and fatty degeneration.
Clinically, the red blood cells or erythrocytes were noted to increase initially and later decrease, causing the white blood cells to increase which resulted in changes in blood coagulation profiles and/or aplastic anermia.
When these changes happen, the bone marrow is completely devoid of recognisable blood cell precursors. Typical symptoms seen when such changes in the blood profiles occur may include light-headedness, headache, loss of appetite, and abdominal discomfort.
With more severe intoxication, there may be weakness, blurring of vision, and difficulty in breathing upon exercise. The mucous membranes and skin may appear pale, and a haemorrhagic tendency may result in easy bruising, epistaxis and bleeding from the gums.
Accumulated case reports and epidemiologic studies in humans suggest the tendency of benzene to cause leukaemia. The development of leukaemia from such exposure tend to be acute and myeloblastic in type, often following aplastic changes in the bone marrow.
One study indicated a five-fold excess of all leukaemias and a 10-fold excess of myelomonocytic leukaemia among benzene-exposed workers in the US Caucasian male population. Among shoemakers chronically exposed to benzene, the annual incidence of leukaemia was 13.5 per 100,000 population, whereas the incidence in the general population was six per 100,000 population.
Four cases of acute leukaemia were reported in shoemakers exposed to concentrations of benzene up to 210ppm for six to 14 years; two to four shoemakers had aplastic anaemia prior to leukaemia; three of the cases were acute myeloblastic leukaemia; the fourth patient developed thrombocythemia in the second year after an episode of aplastic anaemia and acute monocytic leukaemia developed later.
Persons with aplastic anaemia as a result of benzene exposure have been found to be at a much greater risk for developing leukaemia. A follow-up of 51 benzene-exposed workers with abnormal high white blood cells revealed 13 cases of leukaemia. The cumulative incidence of leukaemia among people with clinically ascertained benzene exposure has ranged from 10 per cent to 17 per cent in various studies.
An international organisation of the World Health Organisation, International Agency for Research on Cancer, has concluded that epidemiologic studies have established the relationship between benzene exposure and the development of acute leukaemia and that there is sufficient evidence that benzene is carcinogenic to humans.
A risk assessment of the mortality experience of rubber workers suggests exponential increases in relative risk (of leukaemia) with increasing cumulative exposure to benzene. There was also a statistically significant increase in death from multiple myeloma, although the numbers were small. - National Posion Centre
