Saturday, February 10, 2007

Effects of occupational exposure on the reproductive system: core evidence and practical implications

Occupational Medicine 2006; 56: 516-520.
Burdorf Alex, Figa-Talamanca Irene, Jensen Tina Kold and Thulstrup Ane Marie

Key messages:

  • The reproductive system of both women and men can be affected by occupational exposure and for most health effects both maternal and paternal exposure may be a relevant route.
  • The interpretation of an association between an occupational exposure and a reproductive health effect is almost always hampered by the fact that many adverse outcomes may be caused by multiple (work-related) factors, making it extremely difficult ot attribute a particular outcome to a specific occupational exposure.
  • Occupational exposure may only be relevant during specific time windows, for example shortly before conception or during early pregnancy.

Summary of the core findings:

Physical factors

Ionizing radiation: Spontaneous abortion - Congenital defects - Reduced sperm count / Azoospermia

Noise (> 90 dB(A)): Spontaneous abortion / Low birth weight / Pre-term birth

Heat: Reduced sperm count

Chemical agents

Lead: Low birth weight - Neural tube defects - Reduced sperm count

Mercury: Spontaneous abortion

Organic solvents: Spontaneous abortion

Tetrachloroethylene: Spontaneous abortion - Cleft lip/palate

Glycol ethers: Spontaneous abortion - Reduced semen quality

Dibromopropane: Menstrual disturbances / Spontaneous abortion - Neural tube defects - Reduced semen quality

Ethylene oxide: Pre-term birth / Spontaneous abortion - Cleft lip/palate

Anaesthetic gases: Spontaneous abortion

Antineoplastic drugs: Spontaneous abortion

Pesticides: Reduced sperm count / Azoospermia

Ethylenedibromide: Neural tube defects / Cleft lip/palate - Reduced sperm count / Azoospermia

Carbon disulfide: Reduced quantity and quality of semen

Specific types of welding: Reduced quantity and quality of semen

Psychosocial factors

Irregular work hours: Spontaneous abortion / Menstrual disturbances

Stress: Spontaneous abortion / Pre-term birth

Physical load

Heavy physical work (high energy expenditure): Spontaneous abortion / Low birth weight

Frequent heavy lifting: Pre-term birth / Spontaneous abortion

Prolonged standing: Low birth weight / Pre-term birth / Spontaneous abortion

Both maternal and paternal occupational exposures to ionizing radiation and heat have been established as risk factors for fertility problems.

Limitations in interpretation:

Many uncertainties still exist as to the interpretation of the evidence presented.

A core issue is, undoubtedly, the exposure assessment in epidemiological studies.
In most studies: self-reported job titles (questionnaires)
This assessment strategy is far too crude to establish a meaningful insight into the magnitude and duration of the specific exposure responsible for the observed health effect.

Some occupations have been consistently associated with reproductive effects (e.g. hairdressers, greenhouse workers), but is remains difficult to identify the specific risk factor since in most workplaces these workers are exposed to a mixture of different risk factors and different chemical compounds.
This severly limits the evaluation of the exposure-response relationship for single risk factors.

It is well-established that maternal exposure in the few months before conception is important for fertility and that teratogenic effects may arise during the organogenesis phase during the first 3-8 weeks of pregnancy.
However, long-term exposure may also be relevant for example germ line DNA modifications, or where the agents are biopersistent and accumulate in body fate, such as several pesticides.

Appropriate time windows of highest susceptibility are not well-established for most occupational hazards, which hampers clear advice as to when preventive measures should be undertaken.

A specific feature of reproductive health is that the causal pathway of hazardous exposure in occupations may be female- or male-mediated.

There is extensive evidence from animal studies for male-mediated developmental effects (e.g. spontaneous abortions, growth retardation, malformations, behavioural abnormalities) of environmental agents .

Occupational exposures are generally lower today than they were years or decades ago. Changes in the production process and control measures have had a noticeable impact on exposure levels. In addition, toxic substances may have been replaced by less toxic agents (e.g. PER partly replaced by TCE).
One has to bear in mind that industries may have outsourced the most dirty jobs towards less developed countries or less well-protected small enterprises.

In conclusion, the available evidence presented in this issue of Occupational Medicine, does not allow to derive clear exposure-response relationships.
It remains difficult to arrive at sound conclusions as to the amount of exposure that will require control measures to prevent the occurence of adverse effects on the reproductive system.

Practival implications for occupational health:

The occupational health professional is faced with difficult questions regarding the necessary measures to be taken to ensure that health effects on the reproductive system will not occur.

In general, the precautions to be taken for the protection of the reproductive health of both women and men will not differ form the safeguarding of all workers.

European Union - European Directive 92/85/EEC

Detailed guidelines on the requirements with respect to physical, chemical and biological agents, and industrial conditions including physical load, mental and physical fatigue, and physical and mental stress.


The evidence on occupational risk factors for adverse effects on the reproductive system is consistent for a limited number of risk factors, most notably exposure to lead, glycol ethers, organic solvents, pesticides and ionizing radiation.

It remains difficult to arrive at sound conclusions on the level of exposure and the specific chemicals within the groups of glycol ethers, organic solvents and pesticides that are associated with an increased risk.

Precautions to be taken for the protection of the reproductive health of both women and men have traditionally focused on pregnant women in the workplace.

The available evidence strongly suggests that exposure in the few months before conception may be of importance too, both among women and men.

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