Capacity to cause harm

In the following I make suggestions for how we should assess this capacity to cause harm. I then discuss three other features of synthetic chemicals — novelty, persistence and mobility - that have a bearing on how reliable we should consider our knowledge about a chemical to be and the degree of reliability that we should seek. In Chapter 10 1 discuss how assessments of riskiness could function in regimes for regulation of chemicals. 

When deciding how risky a chemical is, this information on the capacity to cause harm needs to be considered along with other relevant aspects of the chemical, not in isolation. How we could regulate on the basis of riskiness is a matter I discuss in Chapter 10. 

The degree of risk depends on our exposure to a chemical, which may be affected by our behaviour, but riskiness just depends on the nature of the chemical and what we know about it. The hazardousness of a chemical (its capacity to cause harm) is one thing that contributes to its riskiness, but a chemical is also more risky if it is novel and we do not have a full understanding of how it fits into natural processes and cycles and if it is persistent or mobile. 

Whether a chemical substance is naturally occurring should affect where the burden of proof lies. At one end of the scale are substances identical to common natural ones. For these the burden of proof should lie with the regulator to show that they have the capacity to cause harm. Regulatory controls on them should then depend on the nature of the harm that they have the capacity to cause. At the other end are chemicals that are clearly novel. These should be assumed to be risky unless there is good evidence that they are accommodated in natural processes without significantly changing those processes or causing harm. 

Capacity to cause harm is inherent in drugs in a way that sets them apart from other manufactured products and harm often occurs in the absence of fault. 

Dangerous parts eliminate, or reduce capacity to cause harm ... 

Safety practitioners have often debated the expression potential hazard and have come to the conclusion that there is no such thing as a potential hazard. They argue that a hazard is a hazard is a hazard. They are correct. The term potential hazard really refers to a hazard that has the potential to eause harm. The keyword here is having potential or having the capacity to cause harm. 

In assessing the riskiness of a chemical it would not be important to estimate exposures to the chemical, since unlike risks (the probability of harm being caused by it), how risky a chemical is does not depend on the amount people are exposed to. Risks can be reduced by strategies that reduce exposure (such as not eating food from contaminated environments), but these do not change the capacity of the chemical to cause harm, and thus its riskiness. 

The capacity of a chemical to cause harm is what the hazard identification stage of risk assessment is intended to identify - the hazards of a chemical are the adverse effects [harm] which [it] has an inherent capacity to cause (Article 2 of Directive 93/67/EEC). The identification of adverse effects on the health of humans and wildlife relies heavily on tests on laboratory animals. I have already discussed some of the many uncertainties that result from the use of animal tests. A key question is whether there are viable alternatives. Before proposing an alternative testing strategy I first consider animal tests as scientific experiments and ask whether they are good experiments, given what we want to find out. 

These methods do not, of course, provide certainty with regard to the probability that a particular level of exposure to a chemical will cause harm, but neither do the current animal test methods. What they do provide is information on more limited questions, questions about the capacity of the chemical to initiate changes which have the potential to cause harm to the organism. This information is, I suggest, more relevant to chemicals regulation than that provided by animal experiments, because it is of more general applicability. It is less likely to give the false reassurance of non-hazardousness that is provided by an animal test where the animal tested happens not to be susceptible to the chemical, while the species we are concerned about is. 

The types of harm that chemicals have the capacity to cause (in other words their hazards) are qualitatively different and not commensurate with each other. At one extreme are effects that require reasonably high concentrations of the substance, are immediate and localized (for example flammability, explosivity, corrosiveness and acute toxicity). The causal relationship between a particular chemical exposure and such effects is usually obvious, or at least easy to demonstrate. Those affected generally include those who deal directly with the chemical and it is often possible to handle and store the chemical in such a way that harm is avoided. The existing European Union (EU) regulatory system, dating from the 1967 dangerous substances directive (Council Directive 67/548/EEC) was clearly set up with... 

Another important distinction is the difference between hazard and risk. The two terms are sometimes used as synonyms. In fact, hazard is a much more complex concept because it includes conditions of use. The hazard presented by a chemical has two components 1) its inherent capacity to do harm by virtue of its toxicity, flammability, explosiveness, or corrosiveness and 2) the ease with which the chemical can come into contact with a person or other object of concern. Together, two components determine risk (i.e., the likelihood or probability that a chemical will cause harm). Thus, an extremely toxic chemical, such as strychnine, cannot cause poisoning if it is in a sealed container and does not contact the handler. In contrast, a chemical that is not highly toxic can be lethal if a large amount is ingested. 

The reproductive systems of both males and females can be harmed by particular chemicals. In males certain chemicals cause the testes to atrophy and reduce or eliminate their capacity to produce sperm. Particularly striking in this regard is a now banned but once widely used pesticide called DBCP, residues of which persist in ground water supplies in a few regions of the country. Its pronounced impact on spermatogenesis is readily detectable in experimental animals and, unfortunately, has also been observed in some men once occupation-ally exposed to large amounts. The heavy metal cadmium is another substance effective at reducing sperm production. 

Chronic toxicity The capacity of a substance to cause adverse effects or harmful effects in the organism after long-term exposure. 

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