Occupational exposures to nitrous oxide (N(2)0) were measured in numerous dental operatories. In all cases, the National Institute of Occupational Safety and Health (NIOSH) recommended time-weighted average (for one operation) of 25 ppm was exceeded by wide margins (NIOSH considers 50 ppm to be attainable in dental operatories). However, a new risk assessment is necessary to determine appropriate exposure limits. Many of the operatories were not equipped with scavenging systems and none of them used a scavenging device in combination with a local exhaust ventilation system. Scavenging devices and local exhaust ventilation should be used to control nitrous oxide exposures. Leaks in N(2)0 delivery systems, which were found to be commonplace, should also be controlled. Research and development efforts are needed to improve upon the already existing scavenging devices, and provision for local exhaust ventilation needs to be included in the design of dental operatories.

Air Pollutants, Occupational↗

PubMedDate not supplied

Control of nitrous oxide exposures in dental operatories using local exhaust ventilation: a pilot study.

An experimental portable local exhaust ventilation system was installed in three dental operatories where nitrous oxide was used routinely. Standard methods of exhaust ventilation design used in industry to control exposures to toxic airborne substances were applied to the dental operatory setting. The concentration of nitrous oxide in the dentists' breathing zones was measured before and after installation to determine the efficiency of the system in reducing occupational exposures. Results indicate that placement of the exhaust opening and exhaust air flow rate are important in determining the degree of control achieved. After the system had been installed in one operatory, peak exposures declined from over 600 parts per million (ppm) to less than 70 ppm: the time-weighted average exposure was below the NIOSH recommended level of 25 ppm. A permanently installed local exhaust ventilation system modeled after the portable one used in this pilot study may be feasible for most operatories and should not interfere with dental procedures. The results suggest that nitrous oxide exposures can be greatly reduced if dental operatories are equipped with local exhaust ventilation.

Air Pollutants, Occupational↗

PubMedDate not supplied

Sheep farming in Greenland. Its history, managemental practices and disease problems.

The economy of the Greenlandic sheep industry has always operated on a thin edge, the balance being determined by long-term changes in climate and year-to-year weather fluctuations. During the last decades sheep farming has been intensified in many areas, and more rational management systems have been introduced under the guidance of agricultural and veterinary consultants. Improvements include winter feeding, strategic breeding and lambing practices and disease control programmes. Successful efforts are being made to prevent the recurrence of previous dramatic declines in the sheep population and to diminish losses of growing lambs grazing the extensive rangelands. However, the overall disease situation and the effect of environmental stresses on the breeding stock and growing lambs in this unique, subarctic region are far from being fully explored.

Animal Husbandry↗

PubMedDate not supplied

Studies on the helminth parasites of sheep in Southern Greenland.

The nematode population of sheep on Greenland is dominated by Ostertagia circumcincta and three Nematodirus species: N. spathiger, N. helvetianus and N. abnormalis. These results are compared with those for other Nordic countries. Great similarities exist with subarctic Norway but there is a lesser degree of correlation with Iceland and lowland Norway which tend to have a richer spectrum of species. N. helvetianus and N. abnormalis, however, have not been reported from sheep in these countries. The abomasal worm population was remarkable in that it contained specimens with an abomally large body size. The epidemiology of infection followed the pattern recognized throughout Europe with an early-season periparturient rise in the faecal egg-count of the ewe being followed by increasing levels of infection in lambs in late summer. The epidemiology of Nematodirus infections was quite distinct from that seen in most of Europe. Species differences and the cool summer climate were thought to account for this disparity and a hypothesis was advanced to explain the observed pattern of events. Levels of infection were apparently similar in undergrazed and fully-utilized grazing areas. Dosing ewes during the winter (between November to March) eliminated the periparturient egg rise. Lambs could be kept almost worm free by keeping them on clean rangeland and dosing at 3-5 week intervals. A clear weight-gain advantage over conventionally reared lambs was only recorded in one year of the study.

Animals↗