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The design of an aquifer remediation operation is merely a case of practical experience today. The contaminant is flushed out of the soil by means of a system of injection and recovery wells. The time needed and the amount of water that has to be flushed through the soil to reach a certain required concentration are both important. The amount of water is expressed in terms of the so-called flush factor, which is equal to the ratio of the volume of this water and the volume of the pores in the soil to be flushed. The time needed and the. | Human Biomonitoring of Environmental Chemicals Measuring chemicals in human tissues is the gold standard for assessing people s exposure to pollution Ken Sexton Larry L. Needham and James L. Pirkle What chemicals in your daily routine should you be most concerned about The volatile organic compounds from your carpet The exhaust fumes on the road to work The pesticide residues in the apple in your lunch Most of us are exposed to low levels of thousands of toxic chemicals every day. How can a person or a nation decide which substances should be controlled most rigorously One strategy is to go after the largest sources of pollution. This approach certainly makes sense when those pollutants have obvious and widespread consequences such as warming the globe causing algal blooms eroding tire ozone layer or killing off wildlife. But for protecting human health this strategy does not serve so well because the link between a given compound and its biological effects can be difficult to gauge. For epidemiologists to correlate environmental pollutants with health problems they need to know who has been exposed and at what level. This knowledge is exceptionally difficult to gain when there is a lag between exposure and the manifestation of illness. In such cases the data are seldom if ever sufficient to deter- Ken Sexton is a professor of environmental sciences at the University of Texas School of Public Health. Brownsville Regional Campus and past president of the International Society of Exposure Analysis ISEA . Larry L. Needham is Chief of the Organic Analytical Toxicology Branch in the National Center for Environmental Health of the Centers for Disease Control and Prevention CDC and the current ISEA president lames L. Pirkle is the Deputy Director for Science at the CDC s Environmental Health Laboratory. Sexton s address is University of Texas School of Public Health Brownsville Regional Campus RAHC Building 80 Fort Brown Brownsville TX 78520. Internet ksexton@utb.edu mine
