Specifications

2.2.3 Potential Health Effects

A wide variety of health effects have been potentially linked with occupational nitrous oxide

exposure including: reduced fertility, increased incidence of spontaneous abortion, increased

frequency of sister chromatid exchanges (SCE), interference with vitamin B12 metabolism and

audiovisual disturbances. Hoerauf et al. found an increased number of SCE from exposure in

the operating room to an 8 hr TWA of 12.5 ppm. The primary limitation with this study was that

both nitrous oxide and isofluorane were used in the operating room and it is impossible to

determine which was responsible this finding (Hoerauf et al., 1999).

Animal studies conducted in the 1970s and 1980s suggested that nitrous oxide was embryotoxic

and fetotoxic in rats, caused smaller litters, increased incidence of fetal resorption and increased

number of skeletal abnormalities. The main critiques of these studies were the unrealistic

concentrations and duration of exposure the rats were being exposed (for example 24 hrs/day for

5-9 days at 1000 ppm or 15,000 ppm). The exposure levels used were unreasonably high when

compared to levels encountered in occupational settings.

Many studies have found an increased number of SCE in workers exposed to nitrous oxide,

however, the exposure and outcome were often self-reported, had low response rates and

exposure data was lacking in the studies. Questionnaires were often the method used to collect

the data which can lead to possible response and recall bias (Ahlborg et al., 1995). The main

health concern associated with nitrous oxide exposure is an interference with the metabolism of

Vitamin B12. The theory presented by many studies including Suruda et al., 1997, states that the

gas oxidizes the cobalt atom in the Vitamin B12 from Co

to Co

which inactivates Vitamin

B12−dependent enzymes including methionine synthetase and methylmalonyl coenzyme A

mutase. These enzymes are required for Vitamin B12 activity. The Vitamin B12 deficiency is

thought to lead to defective DNA synthesis.

In 1999, a study by Bodin et al. investigated the potential association between shift work and

nitrous oxide exposure and its effects on pregnancy, birth weight and gestational age. This study

used a questionnaire that was sent to the members of the Swedish Midwives Association. The

findings were that nitrous oxide exposure was associated with reduced birth weight and the