Endocrine disruption as a field of research is in its infancy. The number of industrial chemicals which have been shown to influence the development of laboratory animals through endocrine effects is still limited, and interpretation of the results remains a developing art. Nevertheless, the results appear to be of profound importance and liable to shake the foundations of traditional chemical risk assessment.
One such finding was recently published by US researchers headed by Professor Fred vom Saal of the University of Missouri. Low doses of a chemical widely used in the plastics industry caused enlarged prostate glands in male mice exposed in utero - an oestrogenic effect (ENDS Report 266, pp 8-9 ). The researchers were aware of the scientific importance of their findings but ignorant about the commercial implications.
Professor vom Saal's earlier work had shown behavioural differences in mice due to tiny sex hormone differences which result naturally from their position relative to their siblings inside the womb. Both male and female behaviour was permanently altered by differences in the range of one-tenth of a trillionth of a gram. Bisphenol A, they reasoned, can act as an oestrogen and is capable of triggering sensitive hormonal levers in the foetus. Enlarged prostate glands in humans might predispose individuals to prostate cancer in later life.
On the commercial aspects of their work they were soon to be educated by Dow Chemical. Representatives of the company, Professor vom Saal told ENDS, informed him that they were "disturbed" by his plans to publish his work. Bisphenol A, they said, is worth an estimated $1 billion per year to Dow.
Bisphenol A is a "unique and irreplaceable" chemical, one industry source told ENDS, without which epoxy resins and polycarbonate plastics would be impossible. Dow is the third largest manufacturer behind GE Plastics and Shell and ahead of Bayer. Global capacity is currently 1.88 million tonnes, and the US market price of about 55 cents per pound values the industry at $2.2 billion.
The principal uses of polycarbonates are in the construction industry, CDs, car components and computer housings. Epoxy resins are used in adhesives, floorings and coatings. It is bisphenol A's coatings applications in dentistry, water pipe linings and for food contact uses like lining steel cans which have given rise to the greatest concern. Tinned peas have been found to contain an average of 23µg of bisphenol A (ENDS Report 246, p 3 ), and newly applied dental coatings were found to leach up to 931µg of the compound into patients' saliva per hour.
Row in Brussels
When industry representatives, endocrine scientists and environmentalists met in Brussels in May at a meeting called by the Global Legislators' Organisation for a Balanced Environment, the scene was set for an unseemly row. Professor vom Saal left the meeting in no doubt that he believed the developing foetus to have "an incredible sensitivity; if it is affected these effects are irreversible. A single hit by a chemical can have profound effects."
Such effects may occur at very low doses but, paradoxically, increasing the dose may have less effect because of "receptor downregulation" - where the body responds to hormonal over-stimulation by cutting the number of hormone receptors it produces. The result is a dose-response curve shaped like an 'inverse U' - not the straight line assumed in classical risk assessment. "A high dose of hormone has no predictive value for what happens at low doses. This has profound implications for chemical testing," he concluded.
Professor vom Saal went on to launch an attack on industry risk assessments. These assume a linear dose-response relationship and suggest that the maximum tolerated dose of endocrine disrupting compounds may be a million times higher than those which actually produce effects. "There are no safe doses of endocrine disruptors just as there are no safe doses of carcinogens," he said. "The average person has no idea of how little testing is done on chemicals," he added, calling for greater openness on chemical test data on the part of industry.
Industry's only speaker at the Brussels meeting was Dr Alan Poole, representing the European chemical industry association CEFIC and its Endocrine Modulators Steering Group. Industry "shares the concerns" of scientists, he said. Bisphenol A producers have initiated a "very substantial" research programme into endocrine effects.
But in an apparent attack on Professor vom Saal's work, Dr Poole urged: "We need to bring rigour into what we do. Sometimes that rigour isn't always there." "We are being proactive and responsive," he claimed. "If we are not come and tell us. We want to be transparent and open. We want to be good partners in this debate."
Professor vom Saal countered that the chemical industry was not being proactive but reactive. He alleged that CEFIC had refused to cooperate with independent researchers by supplying surplus female animals treated in its experiments which could have been used to study other potential endocrine effects. Although the industry was attempting to replicate his work, its experimental designs were "profoundly flawed" and "would not pass a peer review panel."
Dr Poole retaliated that the intention was not to repeat vom Saal's work. "I don't know if Professor vom Saal is right, but before you turn everything upside down...you had better be damn sure you have got it right," he warned.
Later in May, the row resumed at an IBC conference in London. Here Dr Poole assured delegates that "where data shows that our products are causing endocrine disruption we will be the first group to act." But he went on to question the plausibility of the endocrine disruption hypothesis. He suggested it was an open question whether foetal tissues are "able to regulate endocrine levels like adults," and asked delegates whether it was "biologically plausible that development is so fragile and the oestrogen receptor so naive that survival and reproduction is threatened" by endocrine "modulators".
Dr Poole, who is Dow Europe's Health and Environmental Manager, urged delegates to look on the "positive side" and consider the benefits of bisphenol A: "[The chemicals] are in your cars! They are lighter, you can drive further on less petrol! They are more recyclable!"
He cautioned against taking "preliminary data at face value", and suggested the levels of bisphenol A believed to have effects were "almost undetectable". A similar argument was used by the Association of Plastic Manufacturers in Europe, which found that bisphenol A fed to animals was rapidly eliminated down to undetectable levels. It argued that the compound could not therefore be an endocrine disruptor (ENDS Report 266, pp 8-9 ). Dr Poole warned the meeting: "If you are saying that just one molecule can have an effect then you are going to turn the whole of toxicology upside down."
However, the description of the bisphenol A research as "preliminary" raised hackles among scientists. Professor Louis Guillette of the University of Florida complained: "Industry dismisses our discovery of effects, saying it is not sure they are real." And Professor Wade Weshons, one of vom Saal's co-workers, later told ENDS that the effects of bisphenol A on the prostate glands of mice have been confirmed by published work in another laboratory - a rare example of endocrine research withstanding the test of reproducibility.
A representative of the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) addressed the London meeting on its Environmental Oestrogens Task Force and its wildlife working group. Dr Tom Hutchinson of Zeneca's Brixham Laboratory told the meeting: "We do not feel that the demonstration of mechanistic effects [of endocrine disruptors] are adverse," since such effects "need to be seen in the context of the environment - which does not see mechanisms." American alligators were no longer classified as endangered species, he noted, and despite vitellogenic effects in fish, river quality in the UK had improved in recent years. The apparent implication was that the potential for endocrine effects can be disregarded as long as wildlife populations appear to be thriving.
Professor Louis Guillette answered that it was necessary to consider population trends very carefully. His long-term studies of alligators in Lake Apopka, which was polluted by a spill of persistent organochlorine pesticides in 1980, showed that the population crashed several years after the spill and then slowly began to recover, but then showed further declines in the mid-1990s. The variation was so great that short-term studies would come to erroneous conclusions about the state of the population, he said.
Defining endocrine effects
One industry delegate questioned whether the prostate effects of bisphenol A in mice could be considered biologically significant because the 30% increase in size induced by the treatment was within the normal range of variation seen between individuals. The point is important since the most widely accepted definition of endocrine disruption in Europe refers to "adverse effects". The definition agreed at a recent meeting in the UK called by the European Commission was: "An endocrine disruptor is an exogenous substance that causes adverse health effects in an intact organism, or its progeny, consequent to changes in endocrine function."
Professor Guillette said that changes within the normal range of a parameter could nevertheless be adverse for individuals and in terms of the population. There are often biological constraints which prevent extremes of variation from being manifest, and changes in population means and variation needed to be considered in deciding whether effects were adverse.
However, Dr Poole did not accept that action was needed on bisphenol A. He told delegates in London that "industry has no interest in selling products which are causing deleterious effects," and if results "proved reproducible" chemicals would be phased out. But he added: "Do we believe that bisphenol A at low doses is causing adverse effects? No, we do not. Do I believe that people are currently at risk? I don't think so."
Dr John Ashby of Zeneca's Central Toxicology Laboratory put a different view. He believes bisphenol A to be an endocrine disruptor "by common perception", but added that the issue of adverse effects was probably secondary. During animal testing the number of effects produced was "alarming", although many were at low levels of significance or were not repeatable, and some were secondary to other effects or artifacts due to changes in body weight. The "adverse effects" phrase had been inserted to signal the need to think about what the effects actually meant.
Nevertheless, he expressed misgivings about the way the term endocrine disruptor was being used. "I fear that an endocrine disruptor will be anything that does anything in any endpoint," he said. "We don't have anything that is not an endocrine disruptor at present - that's cause for thought, I think."
The repeatability of endocrine effects is proving to be a major scientific problem. The issue has become a sensitive one since two laboratories have failed in their attempts to repeat experiments which showed large synergistic effects between oestrogenic pesticides in a yeast cell assay (ENDS Reports 257, pp 5-6 and 266, pp 8-9 ). The reason for the discrepancy remains a mystery.
Dr Ashby delivered a further shock to the scientific community. He said he had been "totally unable to repeat" results published by Dr Richard Sharpe in 1995 which showed that male rats exposed in utero to two industrial chemicals, butyl benzyl phthalate and octyl phenol, had reduced sperm counts and smaller testes (ENDS Report 251, pp 8-9 ). Dr Sharpe had been involved in the work and was equally puzzled by the findings, he said.
"I find it alarming that things are not repeating", Dr Ashby said. "It is not bad science". Changing the laboratory in which experiments are done "changes fifty variables", he suggested, particularly animal food.
Professor Ana Soto of Tufts University, Boston, suggested that variation in animals' food intake would produce endocrine effects because laboratory rat food contained natural phytoestrogens. Professor Guillette expressed similar worries about repeatability, saying that despite extensive standardisation, endocrine assays in different laboratories had yielded very different results.
Dr Ashby concluded that it was "early days" in endocrine research. He argued against "unsound progress" and said he distrusted the apparent rush to draw conclusions. Such a position may be interpreted as a call for inaction, but the World Wide Fund for Nature (WWF), which has taken a leading role in campaigning on endocrine disruptors, accepts that scientific certainties lie far into the future.
Elizabeth Salter of WWF-UK told delegates in London that the endocrine problem was "extremely urgent". There was sufficient evidence to justify action to reduce the toxic load under the precautionary principle "without waiting for more research". WWF has called on the UK Government, the EC and parties to the North Sea pollution conventions to phase out and eliminate endocrine disruptors within a generation.
In Brussels, WWF urged the European Commission to undertake a "horizontal review" of all Directives which had implications for endocrine disrupting compounds before 2000. It wants the burden of proof to be shifted to chemical manufacturers, and suggests that risk assessment should be redefined as "a methodology for keeping untested chemicals off the market." Chemicals of most concern should be "eliminated in an orderly and timely fashion," WWF suggests, instead of being allowed to remain in commerce until proven harmful.
WWF also wants the EC to force food manufacturers to monitor their products for contamination and the "fullest possible" disclosure of information to the public - including labelling to show where ingredients are not fully tested. And it is urging a phase-out of phthalate plasticisers, nonyl phenols and bisphenol A, and warnings where packaging ingredients may be toxic.
But WWF recognises that the ability accurately to quantify the risks of endocrine disrupting compounds is "probably decades away". It suggests that the only way forward is through pollution prevention at source and clean production techniques in industry and agriculture. WWF particularly favours pesticide reduction programmes such as those in Denmark, the Netherlands and Sweden which have achieved a 50% reduction in active ingredient applied.
One policy development in May occurred at a meeting in Miami of Environment Ministers from the G7 states and Russia to discuss children's environmental health issues. The meeting considered "emerging threats" from endocrine disrupting chemicals, and encouraged efforts to prepare an international research inventory, assess the state of the science, prioritise research needs and coordinate research efforts. Ministers pledged to "develop cooperatively risk management or pollution prevention strategies" as sources and fates of endocrine disruptors are identified.
Suspicion of industry
At the Brussels and London conferences, both scientists and environmentalists called on the chemical industry to provide more funding for the endocrine research effort - but scientists in particular are wary and critical of industry censorship and meddling. Professor Soto told the London meeting: "If people see that studies are funded by the Chemical Manufacturers Association then they suspect bias." Professor Guillette agreed, observing that "most industry sponsored studies have found no effects," while "about 70%" of federally-funded research had produced results.
Professor Wade Welshons told of his concern that "undesirable results may be suppressed" where sums of $100 million a day are at stake. But any suggestion that industry withheld data was dismissed by Dr Poole: "The implications [of disobeying US disclosure regulations] were so bad it doesn't happen, we file information on almost everything. It just doesn't happen." But Professor Vyvyan Howard of the Royal Microscopical Society told ENDS of his suspicions that the chemical industry wants to control the direction of research to ensure that "certain questions are not asked."
In Brussels, it emerged that the industry's plans to fund endocrine research through the European Science Foundation - an alliance of national research funding bodies - had fallen through, allegedly because the industry "wanted to be in control" of the direction of the studies. The suggestion was hotly denied by Dr Poole.
Professor Soto proposed that industry should agree to fund research through independent panels which would ensure that funds are correctly targeted and that methods and objectives are agreed in advance. Similar sentiments were expressed by Professors vom Saal, Guillette and Welshons.
However, there seems to be little prospect that the chemical industry will provide funding on the scale considered necessary by environmentalists. Dr Theo Colborn of WWF, author of Our Stolen Future (ENDS Report 255, pp 18-19 ), told the Brussels meeting that $100 million was needed every year. In Europe, CEFIC has agreed to spend only $7 million over three years, while in the USA the chemical industry has committed some $20 million.
The scale of industry's response provoked an outburst from Italian MEP Carlos Pimenta at the Brussels meeting. "You make a billion dollar profit and you offer $7 million for research!" he shouted, leaving his seat. "It's obscene!"