Air pollution and Health NEJM

[Guest guest]

Mags USA

Good health comes at a price, we need to pay the price!

~~~~~~~~~~~~~~~~~~~~~

The New England Journal of Medicine

December 14, 2000

Vol. 343, No. 24

http://www.nejm.org/content/2000/0343/0024/1742.asp

Fine Particulate Air Pollution and Mortality in 20 U.S. Cities,

1987-1994

M. Samet, Francesca Dominici, C. Curriero, Ivan Coursac,

L. Zeger

Abstract

Background.

Air pollution in cities has been linked to increased rates of mortality

and morbidity in developed and developing countries. Although these

findings have helped lead to a tightening of air-quality standards,

their validity with respect to public health has been questioned.

Methods.

We assessed the effects of five major outdoor-air pollutants on daily

mortality rates in 20 of the largest cities and metropolitan areas in

the United States from 1987 to 1994. The pollutants were particulate

matter that is less than 10 µm in aerodynamic diameter (PM10), ozone,

carbon monoxide, sulfur dioxide, and nitrogen dioxide. We used a

two-stage analytic approach that pooled data from multiple locations.

Results.

After taking into account potential confounding by other pollutants, we

found consistent evidence that the level of PM10 is associated with the

rate of death from all causes and from cardiovascular and respiratory

illnesses. The estimated increase in the relative rate of death from all

causes was 0.51 percent (95 percent posterior interval, 0.07 to 0.93

percent) for each increase in the PM10 level of 10 µg per cubic meter.

The estimated increase in the relative rate of death from cardiovascular

and respiratory causes was 0.68 percent (95 percent posterior interval,

0.20 to 1.16 percent) for each increase in the PM10 level of 10 µg per

cubic meter. There was weaker evidence that increases in ozone levels

increased the relative rates of death during the summer, when ozone

levels are highest, but not during the winter. Levels of the other

pollutants were not significantly related to the mortality rate.

Conclusions.

There is consistent evidence that the levels of fine particulate matter

in the air are associated with the risk of death from all causes and

from cardiovascular and respiratory illnesses. These findings strengthen

the rationale for controlling the levels of respirable particles in

outdoor air. (N Engl J Med 2000;343:1742-9.)

= - = - = - = - = - = - = - = - = - = - = - =

The New England Journal of Medicine -- December 14, 2000 -- Vol. 343,

No. 24

http://www.nejm.org/content/2000/0343/0024/1798.asp

Editorial

Particulate Air Pollution and Mortality -- Clearing the Air

In the years after World War II, several episodes of severe air

pollution in the United States and Britain aroused public concern about

the effects on health of air pollutants produced by burning fossil

fuels. ...

In the United States, concentrations of particulate air pollution have

declined since the early 1970s. From 1988 to 1993, the average of the

annual mean PM10 concentrations at 799 sites monitored by the EPA

declined by 20 percent. (1) Despite these improvements in air quality, a

series of studies (2,3,4) reported associations between particle

concentrations and the numbers of deaths per day in several U.S. cities

with mean 24-hour PM10 concentrations well below the standard.

Responding to a substantial body of epidemiologic evidence, the EPA

wrote in 1996 that the " staff can not conclude that the current

standards protect public health with an adequate margin of safety " and

that " fine fraction particles [PM2.5, or particles with a diameter of

less than 2.5 µm] are a better surrogate for those particle components

linked to mortality and morbidity effects at levels below the current

standards. " (1) In 1997, the EPA retained the PM10 standards and

promulgated new 24-hour and annual standards for PM2.5, of 65 and 15 µg

per cubic meter, respectively, based on consistency with the literature

on health effects.

Both the epidemiologic evidence and the new PM2.5 standard have been

criticized. Some observers have asserted that the associations found in

the epidemiologic studies are weak, inconsistent, and attributable to

confounding by weather, other pollutants, or misclassification of the

exposure to particulate matter. (5) They note that many of the studies

were performed by the same small group of investigators, that the study

cities were not selected systematically, and that the statistical models

varied from study to study.

Arguing that the 1997 standards for ozone and particulate matter did not

have an adequate scientific basis, industry groups sued the EPA in the

Court of Appeals for the District of Columbia. In 1999, the court

blocked implementation of the 1997 standards. In its current session,

the Supreme Court is hearing an appeal of this decision by the EPA.

A key issue before the Court is whether the cost of compliance can be

considered in setting the standard. The EPA has estimated that

compliance with the 1997 standards for PM2.5 and ozone will require an

investment of about $10 billion per year to modify power plants, diesel

trucks, and other sources of these pollutants (6) and will result in

health benefits with an estimated value of $20 billion to $100 billion

per year. Others have estimated that the costs of compliance could be as

high as $60 billion per year. (7) Thus, the Supreme Court's decision

could have substantial consequences for the economy and the public's

health. Given these stakes, the public and the scientific community need

more and better information about the health effects of particulate air

pollution.

The study reported by Samet et al. (8) in this issue of the Journal

(along with the more extensive investigation from which it is derived

(9)) strengthens our understanding of the epidemiologic evidence and

addresses the criticism of earlier work. The investigators used a single

analytic approach to examine the association between PM10 concentrations

in a given 24-hour period and the numbers of deaths reported on the

following day in 20 of the largest cities and metropolitan areas in the

United States. Samet et al. found an average increase in the rate of

death from all causes of about 0.5 percent for every increase in the

PM10 concentration of 10 µg per cubic meter.

The PM10 concentrations were positively associated with daily mortality

rates in most of the 20 cities studied and at concentrations well below

the current 24-hour standard of 150 µg per cubic meter. In fact, the

90th percentile of the distribution of daily values was below the

24-hour standard in each of the 20 cities. Moreover, the association was

specific to PM10. The concentrations of other regulated air pollutants

produced by the combustion of fossil fuels (sulfur dioxide, nitrogen

dioxide, and carbon monoxide) were weakly and inconsistently associated

with daily mortality rates. Though ozone concentrations were positively

associated with daily mortality rates during the summer months, this

relation did not influence the association between the PM10

concentration and the daily mortality rate. Finally, the finding of a

strong association between the PM10 concentration and the rate of death

from cardiovascular and respiratory causes offers support for the idea

that the concentrations of particulate air pollution influence

mortality.

The findings of Samet et al. are consistent with those of time-series

studies in Europe (10) and cohort studies in the United States. (11)

Thus, the evidence in support of an association between the

concentration of particulate air pollution and the mortality rate is

consistent, is not affected by differences in statistical methods, and

can be generalized.

There are important gaps in both the scientific evidence of causation

and the scientific basis for the regulatory response. The most important

is our inability to explain how fine particles affect health. Some

studies have found that the daily mortality rate is associated with the

concentration of fine particles (PM2.5) but not coarse mass (PM10 -

PM2.5). (12) These findings are consistent with the evidence that fine

particles penetrate indoor spaces, are chemically active, and are

deposited in the respiratory bronchioles and alveoli. Yet little is

known about the specific constituents or characteristics of PM2.5 that

adversely affect health. Moreover, although the standard proposed in

1997 is based on concentrations of PM2.5, most of the epidemiologic

evidence has been obtained from measurements of PM10 or other, less

relevant indicators. Lacking knowledge of the harmful constituents of

fine particles and the mechanisms by which they affect health, the EPA

continues to propose standards based on particle mass.

The epidemiologic evidence suggests that the association between

fine-particle concentrations and mortality is linear across the entire

range of current concentrations. Although substantial reductions can be

achieved at a reasonable cost, a reduction in 24-hour exposures to

levels consistently below the current range would be prohibitively

costly, if not impossible, in the foreseeable future. An aggressive

research program to identify the harmful components of PM2.5, their

sources, and the mechanisms of their effects offers the best hope for

developing more focused regulatory strategies that will simultaneously

protect the public health and the nation's prosperity. In the meantime,

these results present a challenge to policy makers who are required to

protect the public's health with an adequate margin of safety.

H. Ware, Ph.D. Harvard School of Public Health Boston, MA 02115