An updated portrait of the nation’s contact with chemicals in the environment is pretty and ugly at the same time. The population’s exposures to lead, secondhand cigarette smoke, and certain other harmful substances show a decline, for example, but first-time measurements of a number of contaminants reveal them to be widely spread through the population.
In its Third National Report on Human Exposures to Environmental Chemicals, the Centers for Disease Control and Prevention (CDC) in Atlanta assesses the prevalence of 148 chemicals in blood and urine samples collected in 2001 and 2002. The thousands of participants, age 1 year and up, represent a cross section of the U.S. public. CDC’s last such effort, published in 2003 and based on samples from 1999 and 2000, looked at 116 contaminants (SN: 2/22/03, p. 120: Available to subscribers at http://sciencenews.org/articles/20030222/bob9.asp).
The new study and its predecessors didn’t attempt to evaluate any chemical’s toxicity. “For the vast majority of chemicals in the study, we have no evidence of health effects,” says CDC Director Julie L. Gerberding.
Chemicals that do raise concerns include lead, cigarette-smoke components, and mercury. The data reveal a decrease in lead exposure among all age groups. In children 1 to 5 years old, the group with the highest blood concentrations of lead, the average reading fell from 2.23 micrograms per deciliter (µg/dl) of blood in the last report to 1.70 µg/dl in the new one.
Between the second and third CDC reports, the average blood concentration of mercury in women of childbearing age fell 18 percent, to 0.83 µg/dl. There was no significant decline in children, who can be exposed to the neurotoxin before and after birth. While no woman in the study had a concentration as high as what environmental scientists would agree poses a definite danger to a fetus, 5.7 percent of the women had exposures that some scientists argue signify danger, says CDC’s Jim Pirkle.
The CDC report also details evidence of declining exposures to secondhand cigarette smoke. Blood concentrations of cotinine, a breakdown product of nicotine, have dropped by 68 to 75 percent in various age groups since a previous CDC study examined data covering 1988 to 1991.
Other new data indicate widespread exposures to some contaminants not previously included in the survey. More than a quarter of the urine samples contained the polycyclic aromatic hydrocarbon called benzo(a)pyrene. This putative carcinogen arises during combustion. Furthermore, a majority of people showed exposure to diisobutyl phthalate. A study has linked this plasticizer to subtle genital abnormalities in boys (SN: 6/4/05, p. 355: http://sciencenews.org/articles/20050604/fob1.asp).
The high prevalence of so many chemicals highlights the need to understand how mixes of pollutants affect health, says David O. Carpenter, a public health researcher at the State University of New York at Albany.
Some chemicals measured in the previous CDC reports raise concern because of recent evidence that low concentrations can cause harm. For example, CDC says that about 5 percent of people may have enough cadmium exposure to injure the kidneys.