The Population Equation
The earth is currently home to 5.7 billion inhabitants, an increase of almost 5 billion people over the last 200 years. At current rates, 1 billion people will be added to the world population every 11 years. Some say it is only a matter of time before the world's limited resources are exhausted, as trends already show there is less land available for agriculture, less water fit to drink, and less protective ozone as increasing numbers of people struggle for survival and human endeavors destroy the environment. Others remain confident that human innovation and technology will compensate for environmental losses and shortages of resources. In the first Focus article, ecologists, demographers, sociologists, and others take a look at what more of us means.
Living with Livestock
The summer of 1995 may be remembered as the summer of livestock waste spills, in North Carolina and Iowa, at least. As waste flowed into streams, ponds, and rivers during a total of nine waste lagoon spills, the public was awakened to the problems of disposing of animal waste in the fast-growing but little-regulated livestock industry. The second Focus article examines the problems of people living near cattle, hog, and chicken operations, the impact on the environment of livestock waste accidents, and the measures being taken to address these problems.
Nature's Kidneys
A new field of research is showing that sometimes nature provides the solutions for the problems humans create. Scientists are now investigating the use of plants to clean up soil and water contaminated by heavy metals, organic compounds, explosives, and radioactive materials (Innovations). Phytoremediation is a growing area of research, and, although researchers must still address issues like insect pests, animal predators (through which toxicants could be passed into the food chain), and the need for additional chemicals such as chelating agents, plants such as poplar trees, Indian mustard, turnips, and grasses are already showing promise as a cleaner, faster, and cheaper way to remediate waste sites.
Good Health around a Coal-Fired Power Plant
The potential short-term health effects of living near a coal-fired power plant in Israel were studied by collecting personal and environmental data over 10 years from clinics and adjacent air pollution monitoring stations. Goren et al. found that there was no discernable relationship between sulfur dioxide levels emitted from the power plant and respiratory complaints or flu epidemics; air pollution levels were low and did not cause adverse health effects.
Genetic Control of Cadmium Tolerance in Fruitflies
A study by Maroni and Theodore with a transgenic line of fruitflies showed that strains with two copies of the metallothionein allele Mtn3 were more tolerant to cadmium than those with one copy of the gene. However, comparison of gene expression in a strain with one Mtn3 allele to a strain with the Mtn1 allele did not change cadmium tolerance, even though the latter is threefold more expressive. The authors propose that this unexpected finding was due to changes in amino acid substitution in the genes.
Fetotoxic Effects of Wood Preservatives
A cohort of pregnant teachers exposed to wood preservatives in daycare centers was evaluated for potential adverse health effects on the fetus. Karmaus and Wolf conducted interviews and evaluated reproductive histories and report that exposure to pentachlorophenol, hexachlorocyclohexane, and polychlorinated dibenzo-p-dioxins and -furans from wood paneling and indoor air was associated with a reduction in birth weight and length of newborns.
Pesticides around Farm Homes
Even when not directly involved in farm work, children of agricultural families are more likely to be exposed to agricultural chemicals. Simcox et al. sampled household dust and soil from farm homes around Washington State fruit orchards. The authors report residues of four commonly used organophosphate pesticides in 62% of the household dust sample, and greater than 1000 ng/g of at least one organophosphorus chemical in two-thirds of the farm homes. There was no indication of risk of acute intoxication, but the study suggests that exposure to low-level residues of azinphosmethyl occurred throughout the fruit-growing region.
Xenoestrogens Reduce Size of Rat Testes and Sperm Count
Female rats were exposed to low doses of octylphenol or butyl benzyl phthalate during gestation, as were male offspring during the first 21 days of postnatal life. Sharpe et al. report that low doses of these environmental estrogens resulted in reduced testicular size and reduced daily sperm production in rats when they were examined at adulthood 70 days later. The authors hypothesize that these responses are due to a reduction in Sertoli cell numbers and suggest that falling sperm counts recently reported in humans might possibly be associated with similar exposure to xenoestrogens.
Radon Risks Lower in Transients
Warner et al. report that estimates of radon-related lung cancer risks are lower than originally thought when residential mobility is taken into account. Because most people move about 10 times during their lives, potential exposure in the 7% of homes with elevated radon is actually well below levels that would result in elevated risks for lung cancer. As a result, current suggestions for remediating homes with elevated radon levels will benefit future rather than present occupants, and knowledge of current exposure to radon is not necessarily a useful indicator of risk.
Hormonal Reduction of Bone-to-Blood Lead Transfer
Webber et al. (p. 1150) examined postmenopausal women to determine if hormonal replacement therapy would help retain lead stored in bone. After calcium supplementation and hormone replacement therapy for 4 years, lead content of bone was higher in treated women than in women not receiving therapy. The authors suggest that women more likely to release lead from bone into the circulation and suffer potential toxicity include those that have previously accumulated high lead concentrations, have undergone significant perimenopause increase in bone turnover and mineral exhange, and that have an insufficient calcium intake.
Last Update: November 27, 1995
