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Biomedical subjects

R L Maynard

Publications and source records attributed to R L Maynard.

At least 19 recordsLinked to original sources
PubMed2005

Polluted air--outdoors and indoors.

Many air pollutants which are considered important in ambient (outdoor) air are also found, sometimes at higher levels, in indoor air. With demanding standards having been set for many of these pollutants, both in the workplace and ambient air, consideration of the problems posed by indoor pollution is gaining pace. Studies on exposure to pollutants found in the indoor domestic environment are increasing and are contributing to an already significant compilation of datasets. Improvement in monitoring techniques has helped this process. Documented reports of fatalities from carbon monoxide poisonings are still worrying. However, studies on health effects of non-fatal, long term, low dose, indoor exposure to carbon monoxide and other pollutants, are still inconclusive and too infrequently documented. Of particular concern are the levels of air pollutants found in the domestic indoor environment in developing countries, despite simple interventions such as vented stoves having shown their value. Exposure to biomass smoke is still a level that would be considered unacceptable on health grounds in developed countries. As in the occupational environment, steps need to be taken to control the risks from exposure to the harmful constituents of indoor air in the home. However, the difficulty regarding regulation of the domestic indoor environment is its inherent privacy. Monitoring levels of pollutants in the home and ensuring regulations are adhered to, would likely prove difficult, especially when individual behaviour patterns and activities have the greatest influence on pollutant levels in indoor air. To this end, the Department of Health is developing guidance on indoor air pollution to encourage the reduction of pollutant levels in indoor domestic air. The importance of the effects of domestic indoor air on health and its contribution to the health of the worker are increasingly appreciated. Occupational physicians, by training and interest, are well placed to extend their interests into the environmental field and to focus on this important area.

Air Pollutants↗
PubMed2000

In vitro toxicology of respirable Montserrat volcanic ash.

OBJECTIVES: In July 1995 the Soufriere Hills volcano on the island of Montserrat began to erupt. Preliminary reports showed that the ash contained a substantial respirable component and a large percentage of the toxic silica polymorph, cristobalite. In this study the cytotoxicity of three respirable Montserrat volcanic ash (MVA) samples was investigated: M1 from a single explosive event, M2 accumulated ash predominantly derived from pyroclastic flows, and M3 from a single pyroclastic flow. These were compared with the relatively inert dust TiO(2) and the known toxic quartz dust, DQ12. METHODS: Surface area of the particles was measured with the Brunauer, Emmet, and Teller (BET) adsorption method and cristobalite content of MVA was determined by x ray diffraction (XRD). After exposure to particles, the metabolic competence of the epithelial cell line A549 was assessed to determine cytotoxic effects. The ability of the particles to induce sheep blood erythrocyte haemolysis was used to assess surface reactivity. RESULTS: Treatment with either MVA, quartz, or titanium dioxide decreased A549 epithelial cell metabolic competence as measured by ability to reduce 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). On addition of mannitol, the cytotoxic effect was significantly less with M1, quartz, and TiO(2). All MVA samples induced a dose dependent increase in haemolysis, which, although less than the haemolysis induced by quartz, was significantly greater than that induced by TiO(2). Addition of mannitol and superoxide dismutase (SOD) significantly reduced the haemolytic activity only of M1, but not M2 or M3, the samples derived from predominantly pyroclastic flow events. CONCLUSIONS: Neither the cristobalite content nor the surface area of the MVA samples correlated with observed in vitro reactivity. A role for reactive oxygen species could only be shown in the cytotoxicity of M1, which was the only sample derived from a purely explosive event. These results suggest that in general the bioreactivity of MVA samples in vitro is low compared with pure quartz, but that the bioreactivity and mechanisms of biological interaction may vary according to the ash source.

Adsorption↗
PubMed1997

Setting air quality standards for carcinogens: an alternative to mathematical quantitative risk assessment-discussion paper.

It has been accepted in many countries that the regulation of ambient air quality should involve the use of health-based air quality standards. Setting standards for air pollutants which are genotoxic carcinogens presents difficult problems to the regulator, in that the prediction of the effects on health of low levels of exposure is suspected to be inaccurate, and is not currently amenable to either experimental or epidemiological verification. In some countries, techniques of mathematical quantitative risk assessment have been adopted to calculate acceptable levels of exposure to, or the unit risk factors for, genotoxic carcinogens. We regard these approaches as unsatisfactory. An alternative approach, based upon a number of argued premises, a strategy which identifies decision points and the cautious application of uncertainty factors, is described.

Air Pollutants↗
PubMed1997

Emergency hospital admissions for respiratory disorders attributable to summer time ozone episodes in Great Britain.

BACKGROUND: There is accumulating evidence from various countries, including the UK, that ground level ozone concentrations are associated with increased daily hospital admissions for respiratory diseases. This paper estimates the impact of ozone episodes on daily hospital admissions for respiratory disease in Great Britain by combining locally based exposure-response relationships with mapped estimates of ozone exposure for the population in the summers of 1993 and 1995. METHODS: For the given years the available ozone measurements were used to construct maps of ozone concentrations for each day. The population exposed to a given concentration of ozone on a particular day was calculated from census data using a geographical information system. The additional hospital admissions for respiratory disease were then estimated using a regression coefficient for London. RESULTS: It is estimated that 0.10% (a total of 184) and 0.35% (a total of 643) of hospital admissions for respiratory disorders during the summers of 1993 and 1995, respectively, can be attributed to levels of ozone above 50 ppb (the recommended air quality standard for the UK). A sensitivity analysis for 1995 found that, if no threshold is assumed, the estimate is increased by about twenty fold (6% of admissions attributable). CONCLUSIONS: The additional hospital admissions for respiratory disease attributable to ozone are very small in both absolute and relative terms if a threshold of 50 ppb is assumed, but this estimate is very sensitive to threshold assumptions.

Air Pollution↗
PubMed1997

Thunderstorm-related asthma--the epidemic of 24/25 June 1994.

BACKGROUND: A large epidemic of asthma occurred following a thunderstorm in southern and central England on 24/25 June 1994. A collaborative study group was formed. OBJECTIVES: To describe the epidemic and the meteorological, aerobiological and other environmental characteristics associated with it. METHODS: Collation of data from the Meteorological Office, the Pollen Research Unit, the Department of the Environment's Automatic Urban Network, from health surveillance by the Department of Health and the National Poisons Unit, from clinical experience in general practice and hospitals, and from an immunological study of some of the affected cases from north east London. RESULTS: The thunderstorm was a Mesoscale Convective System, an unusual and large form of storm with several centres and severe wind gusts. It occurred shortly after the peak grass pollen concentration in the London area. A sudden and extensive epidemic occurred within about an hour affecting possibly several thousand patients. Emergency services were stretched but the epidemic did not last long. Cases had high serum levels of IgE antibody to mixed grass pollen. CONCLUSION: This study supports the view that patients with specific IgE to grass pollen are at risk of thunderstorm-related asthma. The details of the causal pathway from storm to asthma attack are not clear. Case-control and time series studies are being carried out.

Adult↗
PubMed1995

Setting air quality standards for carcinogens: an alternative to mathematical quantitative risk assessment--discussion paper.

1. It has been accepted in many countries that the regulation of ambient air quality should involve the use of health-based air quality standards. 2. Setting standards for air pollutants which are genotoxic carcinogens presents difficult problems to the regulator, in that the prediction of the effects on health of low levels of exposure is suspected to be inaccurate, and is not presently amenable to either experimental or epidemiological verification. 3. In some countries, techniques of Mathematical Quantitative Risk Assessment (MQRA) have been adopted to calculate acceptable levels of exposure to, or the unit risk factors for, genotoxic carcinogens. We regard these approaches as unsatisfactory. 4. An alternative approach, based upon a number of argued premises, a strategy which identifies decision points and the cautious application of uncertainty factors, is described.

Air↗