The New Engineer
This is a final version submitted for publication. Minor editorial changes may have subsequently been made.
The health impacts of environmental pollutants are notoriously difficult to assess, particularly when a mixture of pollutants are involved. Because of the uncertainties and interests involved, legal requirements and standards have sometimes failed to protect public health from industrial pollutants and this is why it is not enough for companies to merely comply with the law. Rather they need to take a precautionary approach which aims to continually minimise pollutants.
The leukaemia cluster in the vicinity of Port Kembla, south of Sydney illustrates the type of health problems that can arise and the complexity of determining their cause. An official investigation, carried out by the Illawarra Area Health Service, identified 13 people resident in the area, under the age of 50 years, had been diagnosed with leukaemia, a form of cancer, between 1989 and 1996. (Six of these people have died.) This rate of diagnosis is 3 or 4 times the average rates in the rest of the region. Of even more concern is the high number of young people involved. In the age group 15-24, the incidence of leukemia was "more than 10 times higher than expected. The probability of observing at least this excess, due to chance alone, is 0.00012 (1 in 8,333)."
The investigation noted that benzene is "the only known leukaemogen with significant local environmental sources." Although residential exposure to benzene has not been proven to cause leukaemia, occupational benzene exposure is an internationally recognised cause of leukemia. The neighbourhood in question is a heavy industrial area with more than its share of industrial pollution. A key industry and major employer in the area is the BHP steelworks. The school where three students and a teacher were diagnosed with leukemia is downwind of the steel works and in particular the coke production area was identified as the main industrial source of benzene.
There were no legal requirements for BHP to monitor its benzene emissions till a 7.30 Report researcher asked to see a copy of BHP's pollution licence in 1996. Since the levels of benzene being emitted from the steelworks had not been monitored before the leukemia cluster was identified the investigation had to rely on BHP estimates of what they had discharged between 1970 and 1996. Given BHP's estimates, the investigation concluded that the amount of benzene in the air was not enough to cause the leukaemia cluster and therefore "with the available information it is not possible to ascribe the cluster to any particular exposure(s)."
However it seems that the synergistic effects of chemical pollution in the area were not investigated, particularly the combination of benzene as a known carcinogen with other chemicals that depress the immune system. Dioxin is one such chemical that weakens the immune system at low levels of exposure. According to the US EPAs recent landmark dioxin risk assessment, background levels of dioxin are causing "decreased sperm count in men, higher probability of endometriosis in women, weakened immune systems, and other health problems" in the American population. Dioxin is also thought to be a cancer promoter, promoting cancers initiated by other chemicals.
The Illawarra Area Health Service investigation noted that the steelworks "are known to be significant sources of dioxins." BHP's annual report shows that it emits the equivalent of 20g of TCDD, the most toxic of the dioxins, per year. Whilst this may not sound like much the US EPA estimates that dioxin emissions in the whole of the USA totalled 3kg of TCDD equivalents in 1995. The World Health Organisation has recommended a "tolerable daily intake" of dioxin of between 1 and 4 picograms per kilogram of body weight per day, that is 26-100x10-9g per year for a 70kg adult.
BHP may not have breached any legal requirements in its emissions of benzene and dioxin but this is little comfort to people living in the vicinity of its Port Kembla steelworks. If engineers want to protect people living around industrial facilities they cannot wait till the effects of industrial pollutants are known for certain, nor assume that legal requirements are sufficient to protect public health. Rather they need to take a precautionary approach that seeks to continually reduce emissions.