Author: Muhammad Ahmad

Particulate matter (PM) is the general term for microscopic solid or liquid phase (aerosol) particles suspended in air. PM exists in a variety of sizes, with diameters ranging from a few angstrom units to several hundred micrometers. Particles are either emitted directly from primary sources or are formed in the atmosphere by gas‐phase reactions (secondary…

Carbon monoxide (CO) is a colorless, odorless gas formed primarily as a by‐product of incomplete combustion. The major health hazard posed by CO is its capacity to bind with hemoglobin in the blood stream and thereby reduce the oxygen‐carrying ability of the blood. Transportation sources account for the bulk (76.6%) of total national CO emissions.…

Risk assessment is built on the principle that small exposures carry with them some risk of an untoward health effect such as development of a malignant tumor or leukemia at some time in the future. Such risks are generally considered to be stochastic or probabilistic in nature and are expressed in terms of a risk…

The final stage of a four‐stage human health risk assessment is to estimate risks. Cancer is not the only undesired health consequence of pollution: exposure to ionizing radiation and coal dust, for example, can lead to radiation sickness and birth defects, as well as cancer. To illustrate risk characterization; however, we shall focus on the…

Broadly speaking, toxicity is the degree to which a substance is poisonous. Most chemicals, toxic or otherwise, enter the body through eyes, respiratory tract, digestive tract, and skin. Two levels of toxicity are defined: acute “short‐term” exposure that initiates poisoning and chronic “long‐period” exposure that causes anemia, leukemia, and death. In the context of the third…

In mechanistic models, it is assumed that a certain number of reactions, events, or “hits” (concept derived from radiation biology), or transition stages, related to a critical target in the cell (DNA), are necessary to transform a normal cell to a cancer cell. These models are important because there seems to be general consensus that…

Measures of ongoing exposure to health risks call for determination of concentration. In the Section 5.1.3.1, Example 5.3 shows how to determine bioconcentration, and Example 5.4 explains the use of slope factors, often used in quantifying risks of cancer. Partition Coefficient and Bioconcentration Factor While extensive research continues to refine existing methods and to develop new markers of exposure and…

Risks to human health may be assessed on the basis of information collected from environmental monitoring; alternatively, the data may be incorporated into models of human activity and exposure, in the workplace and elsewhere, to permit analysts to draw conclusions on the likelihood of adverse effects. In both cases, risk assessment is an essential tool…

The concept of risk, the possibility of loss or injury, is familiar in every human endeavor. Both chemical engineers and environmental engineers routinely consider the risks of adverse health and environmental impacts from exposures to industrial by‐products released to air, water, and land. Risk assessment, thus, is an organized process for describing and estimating the…