Richard K. Miller, Paul Peters, and Patricia R. McElhatton
2.23.1 Solvent exposure in general 564
2.23.2 Formaldehyde and formalin 573
2.23.3 Chloroprene (chlorbutadiene) 574
2.23.4 Cyanide 575
2.23.5 Photographic/printing chemicals 575
2.23.6 Pesticides 576
2.23.7 Phenoxyacetic acid derivatives and chlorinated dibenzo-dioxins 581
2.23.8 Metals 583
2.23.9 Hazardous waste landfill sites 590
2.23.10 Radiation associated with the nuclear industry 592
2.23.11 Video display terminals (VDTs) 594
2.23.12 Mobile phones 596
2.23.13 Other sources of electromagnetic radiation 596
It is ambitious to describe the risk assessment of environmental agents being the sum total of all the substances capable of producing an effect, whether physical, chemical or biological, which make up the surroundings and influence the development of an individual. Synthetic but also naturally occurring substances sometimes have significant pharmacological and toxicological properties; but how many are there? For example, toxins such as chemicals from microorganisms, fungi, plants, and animals have not been analyzed systematically. Millions of synthetic chemicals are registered, but fewer than 100 000 are currently in commercial or industrial use, and most of these chemicals have not been tested for developmental toxicity. The number of synthetic chemicals is likely to continue to increase. Hence, agents selected here might be of importance if there is occupational exposure for women who are pregnant or are in their reproductive years, and include:
■ substances in the home or garden environment
■ those agents we know that do have actions on reproduction (mostly pollutants)
562 2.23 Occupational, industrial, and environmental agents
■ those chemicals about which there arc frequent inquiries at teratology information services.
In principle, it is difficult to distinguish between industrial and environmental chemicals. Environmental pollutants are usually industrial chemicals released as pollutants into the environment during production, use, recycling, and combustion processes, or into air, water or soil from naturally high sources - for example, arsenic in regions with substantial granite deposits. However, the concentration of industrial chemicals may normally be higher in a particular workplace than in the general environment. Moreover, when an accident occurs, the environmental pollution may exceed the usual workplace exposure. Thus, biomonitoring is important in all settings.
A number of reviews have been published on the reproductive toxicity of industrial chemicals (see overviews in Miller 2004, Schardein 2000, Gilstrap 1998, Paul 1993, Sullivan 1993, Barlow 1982), but these cover only a small fraction of the total number of chemicals to which women may be exposed in the workplace.
There is an EU requirement in the Pregnant Workers Directive (92/85/EC) for the production of materials safety datasheets. These sheets should include what information exists on the reproductive toxicity of the chemical, but in practice these MSDS datasheets rarely provide a useful reference source other than identification of the constituents of the product; the same situation holds true for physical and biological agents.
As there is legislation in most developed countries preventing gender discrimination in employment and protecting the rights of women to work during pregnancy, there is a need for adequate information on the possible risks of exposure to chemicals in the workplace. Among the most widely known is the Johnson Controls case in the US, where the US Supreme Court ruled that since there was reproductive toxicity of lead in both males and females, battery production had to accommodate both genders, and also to reduce the exposure to lead levels appropriate Tor both genders. Thus, women gained equal access to better pay, since working in the battery production area was the route to those higher-paid positions. (UAW v Johnson Controls US Supreme Court 89-1215).
However, individual risk characterization is much more difficult with chemical and physical exposure than with a particular drug treatment, because:
• a pregnant woman is rarely exposed to a single compound
■ measuring workplace or environmental/household contamination levels is often expensive and time-consuming
■ workplace measures are often feared because of conflicts with the employer
■ quantifying exposure via inhalation, oral intake or dermal absorption is difficult
• there is a lack of data regarding kinetic properties (absorption, distribution, metabolism, excretion)
■ fetal exposure and kinetic are even less well known
• reference data in the literature (e.g. no observed adverse effect levels - NOAELs) are mostly derived from animal experiments, which have limited relevance for human exposure. There are few substances where NOAELs can be supported with epidemiological data.
Since it is difficult to specify the upper limits of workplace exposure for pregnant women because of the lack of data, the general Occupational Exposure (Standards and Maximum Exposure) Limits (OELs) of the chemical in question are often used. For an overview of global occupational exposure limits (OELs) for over 5000 specific chemicals, see Brandys (2006). OELs are regularly updated in Canada, France, Germany, Japan, Russia, and the United Kingdom; the OEL is the amount of a workplace health hazard that most workers can be exposed to without harming their health. OELs are not, in the main, based upon reproductive health demands. In the USA, the Occupational & Safety Health Administration (OSHA) sets enforceable permissible exposure limits (PELs) to protect workers against the health effects of exposure to hazardous substances. PELs are regulatory limits on the amount or concentration of a substance in the air. They may also contain a skin designation (see www.osha.gov/SLTC/pel). PELs are based on an 8-hour time-weighted average (TWA) exposure.
In accordance with the maternal protection laws in many countries, pregnant women should not be exposed to toxic, infectious, ionizing or carcinogenic substances. However, in practice many workplaces require pregnant women to handle potentially toxic compounds and do not take into account the possibility that workers might already be pregnant. In addition, non-specific symptoms have to be considered when discussing the tolerability of a certain workplace or household contaminant. If pregnant women complain of repeated symptoms in the workplace - such as headaches, emesis, vertigo - this should be taken seriously. Such recurrent disorders can endanger the normal course of pregnancy. As will be noted later in this chapter, pregnant women may have exaggerated responses to exposure simply because they are pregnant. This is often reported in relationship to the nausea and vomiting of pregnancy. For evaluating approaches to exposure during pregnancy, see Miller (2004).
With respect to awareness of an increased risk for birth defects from environmental pollution, birth defect monitoring systems would be of help. However, birth defect monitoring and surveillance systems seldom methodically measure environmental exposure. Only in the case of a cluster with suggestions for pollution-related causation might such studies be performed. Absence of a change in the prevalence of birth defects in a population is not an observation useful to exclude a (new) environmental developmental toxicant per se, since these monitoring systems arc considered too insensitive. On the other hand, in case of a linkage of occupational exposure with reproductive hazards, the epidemiologist has to demonstrate that, without reasonable doubt, reproductive outcome is worse than expected when the mother has a specific occupational exposure, and that this is not due to a confounder such as disease, maternal age, cigarette smoking, etc. (Kälten 1988).
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