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 used by those responsible for making decisions with environmental consequences (APHA 1989; Allen and Shonnard 2002; National Academy of Sciences USA 2006).
The results of environmental risk assessment are generally intended to be incorporated into decisions that affect the public, along with the economic, social, technological, and political consequences of a proposed action. The need for such analytical data is indicated in Table 5.1, which lists selected US laws that require or suggest human health risk assessment before regulations are promulgated. The list is enormous and probably will grow with time.
In contrast to the specific laws addressing concerns about environmental pollutants presented in Table 5.1, Figure 5.1 offers a generalized scheme of the routes by which these pollutants enter the environment, ending with human exposure.
The paradigm for assessing human health risk consists of formulation of the problem, assessment of the exposure, assessment of any toxic effects, and risk characterization (USEPA 2003).
Air Pollution
Air pollution is an important public health issue in the United States and worldwide. The World Health Organization (WHO) estimated that in 2012, over seven million people died (about one‐eighth of all mortalities) from illness related to exposure to air pollutants (WHO 2014). In addition to the human costs, there also financial costs, including higher public health care costs associated with increased hospitalizations, as well as lost productivity. The high frequency of respiratory ailments, as well as the necessity of wearing an antipollution mask to reduce inhalation of pollutants in certain countries, is well documented in news media.
In the United States, concern over air pollution is significant and is going to be one of the most challenging environmental health issues of our time. A 2015 Gallup poll showed that 38% of Americans were concerned about air pollution “a great deal” (Jones 2015). A 2013 study by researchers at the Massachusetts Institute of Technology estimated about 200 000 Americans die prematurely each year because of air pollution, although this toll is brought on by all sources of air pollution – including nonindustrial ones – such as indoor combustion (e.g. automobiles, trucks, etc.) (Chu 2013).
Table 5.1 United States safety, health, and environmental statutes that imply risk assessment.
Source: From National Academy of Sciences (2006), Hoppins et al. (2006), Asante‐Duah (2002), Kammen and Hassenzahl (1999), Roberts and Abernathy (1997) and Federal Focus (1991).
| Environmental Protection Agency | |
| Atomic Energy Act (also NRC) | 42.U.S.C.2011 |
| Comprehensive Environmental Response, Compensation and Liability Act (CERCLA, or Superfund) | 42.U.S.C.9601 |
| Clean Air Act | 42.U.S.C.7401 |
| Clean Water Act | 33.U.S.C.1251 |
| Emergency Planning and Community Right to Know Act | 42.U.S.C.11001 |
| Federal Food and Drug, and Cosmetics Act (also HHS) | 21.U.S.C.301 |
| Federal Insecticide, Fungicide, and Rodenticide Act | 7.U.S.C.136 |
| Lead Contamination Control Act of 1988 | 42.U.S.C.300j‐21 |
| Marine Protection, Research, and Sanctuaries Act (also DA) | 16.U.S.C.1431 |
| Nuclear Waste Policy Act | 42.U.S.C.10101 |
| Resource Conservation and Recovery Act | 42.U.S.C.6901 |
| Safe Drinking Water Act | 42.U.S.C.300f |
| Toxic Substances Control Act | 7.U.S.C.136 |
| Food Quality Protection Act of 1996 | 7.U.S.C.6 |
| Consumer Product Safety Commission | |
| Consumer Product Safety Act | 15.U.S.C.2051 |
| Federal Hazardous Substance Act | 15.U.S.C.1261 |
| Lead‐Based Paint Poisoning Act (also HHS and HUD) | 42.U.S.C.4801 |
| Lead Contamination Control Act of 1988 | 42.U.S.C.300j‐21 |
| Poison Prevention Packaging Act | 15.U.S.C.1471 |
| Department of Agriculture | |
| Eggs Products Inspection Act | 21.U.S.C.1031 |
| Federal Meat Inspection Act | 21.U.S.C.601 |
| Poultry Products Inspection Act | 21.U.S.C.451 |
| Department of Labor | |
| Federal Mine Safety and Health Act | 30.U.S.C.801 |
| Occupational Safety and Health Act | 29.U.S.C.651 |
| Department of Transportation | |
| Hazardous Liquid Pipeline Safety Act | 49.U.S.C.1671 |
| Hazardous Materials Transportation Act | 49.U.S.C.1801 |
| Motor Carrier Safety Act | 49.U.S.C.2501 |
| National Traffic and Motor Vehicle Safety Act | 15.U.S.C.1381 |
| National Gas Pipeline Safety Act | 49.U.S.C.2001 |
Problem Formulation
Problem formulation comprises such activities as definition of the goals and spatial and temporal scale of the ecological risk assessment (ERA), development of a site conceptual model (SCM), and selection of endpoint and nonhuman receptor species. The final step is to identify contaminants of potential concern and to determine whether, for example, threshold limit values (TLVs) have been exceeded. Examples 5.1 and 5.2 illustrate how the results of environmental monitoring of three common industrial pollutants can be used in calculations of the quantities present.
EXAMPLE 5.1 MONITORING
An air sampler collects 16 mg of methyl chloride during 6‐hour work shift. The sampler has the following characteristics:
- Average flow rate = 1.2 l/min
- Collection efficiency = 0.9
What is the eight‐hour total weighted average (TWA) of methyl chloride?
SOLUTION
The total air collected was
Sampler content was 16 mg or 
= 17.8 mg in the air sampled
Methylene chloride concentration in air sampled = 17.8 mg/0.432 m3 = 41.2 mg/m3 (ppm)
Average air concentration during the six‐hour collection time
Was the TLV exceeded?
TWA for methyl chloride is 50 ppm (mg/m3) and was not exceeded.
EXAMPLE 5.2 CONTINUOUS MONITORING
Lead fumes are produced in a lead‐burning operation. A continuous monitor in the work room is operated for five consecutive days. The following are known:
| Initial sample rate | 1 cfm (cubic feet per minute) |
| Final sample rate | 0.7 cfm |
| Filter efficiency | 0.999 for particulates ≥20 μm average mean diameter (AMD) |
| 0.83 for particulates <20 μm AMD | |
| Mass of dust collected | 1.7 g |
| % of lead in dust | 23 |
SOLUTION
Determine the TWA lead concentration in the work air.
Assume approximately linear reduction in sampling rate as filter loads. Hence, average sampling rate is
and total air sampled is
Total dust collected = 1.7 g or 1.7 ∙ 0.23 = 0.39 g of lead, since 23% of dust is lead. Since lead was present as a fume, AMD < 20 μm and total lead collected is
Average lead concentration is the total amount divided by sample volume or
Assuming lead generation occurs only during eight‐hour workday, the TWA is
Dusts pose a particular problem with respect to determining acceptable air concentrations. The particle size distribution needs to be taken into account, and the specific respirable fractions, as published in the literature, must be used to determine exposure. Dust particle sizing can be accomplished by size‐selective samplers, typically multistage impactors.
These sample examples only scratch the surface of techniques used in problem formulation. They are, however, illustrative. Sometimes, as in Example 5.1, monitoring reveals that existing pollution prevention measures are working properly and that no problem exists. Example 5.2 shows that determining the TWA of a pollutant is not always sufficient to formulate a problem.
Leave a Reply