MPH 540 Week 3 Risk Assessment of an Environmental Exposure Example

A Century-Old Smelter and a Toddler's Backyard: Applying the Four Steps of Risk Assessment to Arsenic and Lead in Residential Soil

[Student Name]

University of Phoenix

MPH/540: Environmental and Occupational Health Management

Week 3 Assignment

[Instructor Name]

[Date]

The county, the soil sampling results, exposure assumptions, calculations and decisions are composites written for a model paper; research findings come from the sources cited.

In April, a father on the county's north side called the environmental health office. His neighbor had paid to have her yard tested, and the laboratory reported arsenic well above background. He had a two-year-old who played in the backyard every afternoon. He asked whether his yard was dangerous. The smelter that operated a mile away closed about a century ago, but its emissions settled into the soil of the surrounding neighborhoods. This paper applies the four steps of risk assessment to his question.

The Framework

In 1983, the National Research Council laid out a four-part process: deciding whether an agent can cause harm, relating the size of a dose to the chance and severity of that harm, measuring how much people actually take in and combining these findings into a statement of risk. The report also drew a line between assessment, a scientific estimate of risk, and risk management, the decisions about what to do, which involve costs, values and law (National Research Council, 1983). The distinction matters in the county, because residents need an honest estimate before arguing about cleanup.

Step One: Hazard Identification for Arsenic

Arsenic's effects are well documented. Ingested inorganic arsenic is a known cause of skin cancer, and evidence indicates it also causes cancers of the liver, lung, kidney and bladder (Smith et al., 1992). A later review concluded that chronic arsenic exposure leaves essentially no bodily system untouched, adding skin, developmental, neurological, respiratory, cardiovascular, immune and endocrine effects, and that exposure early in life may raise risks of several diseases in adulthood (Naujokas et al., 2013).

Hazard Identification for Lead

Lead has no known safe level for children and harms brain development, attention and learning. Because smelter soils usually contain both metals, the assessment evaluated them together.

Step Two: Exposure Assessment

Exposure assessment asks who is exposed, by what route, how much and for how long. The team identified young children as the most exposed group, because they play on the ground and put hands and toys in their mouths, and incidental soil ingestion as the main route. Soil also becomes household dust, adding indoor exposure.

Why Soil Matters

Research supports this focus. A review concluded that soil lead is at least as important as intact lead paint as a pathway for children's exposure, that soil and house dust are associated with population blood lead levels in children and that soil lead abatement appeared more effective than paint abatement in reducing children's blood lead (Mielke & Reagan, 1998). A yard can be as dangerous to a toddler as peeling paint, and harder to see.

The Sampling

The state health department sampled 212 yards within two miles of the former smelter. Each yard was divided into play areas, gardens and bare spots, and composite samples were analyzed. Median arsenic was 38 milligrams per kilogram, compared with about 10 in background areas; 41 yards exceeded 60. Median lead was 310 milligrams per kilogram, with 36 yards above 400.

The Father's Yard

Samples from the father's backyard found arsenic at 64 milligrams per kilogram in the play area and lead at 420, both above the median and near the high end of sampled yards.

Exposure Assumptions

For a child aged one to six, the team assumed a body weight of 15 kilograms and incidental ingestion of 200 milligrams of soil and dust per day, a conservative default, 350 days a year. Because not all arsenic in soil is absorbed, the state program applied a default relative bioavailability of 60%.

Calculating the Dose

The daily arsenic dose for the father's child is soil concentration times ingestion rate times bioavailability, divided by body weight: 64 milligrams per kilogram times 0.0002 kilograms of soil per day times 0.6, divided by 15 kilograms. The result is about 0.0005 milligrams per kilogram of body weight per day, adjusted slightly downward for 350 days a year of exposure.

Step Three: Dose-Response Assessment

Dose-response assessment describes how the probability or severity of harm changes with dose. For non-cancer effects, agencies derive a reference dose below which harm is considered unlikely over a lifetime. For cancer, they estimate a slope factor, the added lifetime risk per unit of daily dose, usually assuming no safe threshold. The state program used published federal values for arsenic, including a reference dose of 0.0003 milligrams per kilogram per day.

The Hazard Quotient

Dividing the child's estimated dose by the reference dose gives a hazard quotient of about 1.6. A quotient above 1 does not mean harm will occur, but it signals that exposure exceeds the level considered safe with a margin, warranting action.

Cancer Risk

Cancer risk from childhood exposure is calculated by averaging dose over a lifetime and multiplying by the slope factor. For the father's yard, the estimated added lifetime cancer risk from six years of childhood exposure fell in the range of one in ten thousand, at the upper edge of the range that federal cleanup programs typically consider acceptable.

Lead

Lead is assessed differently. Instead of a reference dose, programs model the probability that a child's blood lead exceeds a level of concern given soil and dust concentrations. At 420 milligrams per kilogram, modeling suggested a meaningful share of young children would exceed the level of concern, consistent with the finding that even low blood lead reduces intelligence.

Step Four: Risk Characterization

Risk characterization pulls the steps together in plain language. For the father, the team explained that arsenic and lead in his play area were high enough that a young child playing there daily for years would face a measurable, avoidable risk, mostly to development from lead and a small added cancer risk from arsenic. The risk was not an emergency, but it justified prompt steps.

Uncertainty

Every step carries uncertainty. Soil ingestion varies widely among children; some eat far more than 200 milligrams a day, and some far less. Bioavailability varies with soil chemistry. Samples may miss hot spots. Reference values include safety factors, and the dose-response relationship for arsenic at low doses is extrapolated from higher exposures. The team reported a range rather than a single number.

Communicating the Risk

Staff met the father at his home, showed him the results on a simple chart comparing his yard with background and explained what they meant without jargon. They offered blood lead testing for his daughter and gave practical steps he could take immediately.

Risk Management

Management decisions followed from the assessment. Interim steps included covering bare soil with mulch or grass, providing a raised sandbox with clean sand, washing hands after outdoor play and removing shoes at the door. For yards above action levels, the state program offered soil replacement: removing the top foot of soil and replacing it with clean fill. Blood lead testing was offered to all young children in the sampling area.

Environmental Justice

The yards with the highest levels were in older, lower-income neighborhoods whose residents had no role in the smelter's emissions a century ago. The program prioritized homes with young children and pregnant residents for replacement.

Conclusion

The four steps of risk assessment turned a father's worried question into an answer: arsenic and lead in his yard pose a measurable and avoidable risk to his daughter. Evidence on arsenic's many health effects and soil's role in child lead exposure framed the hazard, stated assumptions produced a dose and hazard quotient and honest uncertainty shaped the message. Keeping assessment separate from management allowed interim protections and yard replacement to follow from the science.

References

Mielke, H. W., & Reagan, P. L. (1998). Soil is an important pathway of human lead exposure. Environmental Health Perspectives, 106(Suppl. 1), 217-229. https://doi.org/10.1289/ehp.98106s1217

National Research Council. (1983). Risk assessment in the federal government: Managing the process. National Academies Press. https://doi.org/10.17226/366

Naujokas, M. F., Anderson, B., Ahsan, H., Aposhian, H. V., Graziano, J. H., Thompson, C., & Suk, W. A. (2013). The broad scope of health effects from chronic arsenic exposure: Update on a worldwide public health problem. Environmental Health Perspectives, 121(3), 295-302. https://doi.org/10.1289/ehp.1205875

Smith, A. H., Hopenhayn-Rich, C., Bates, M. N., Goeden, H. M., Hertz-Picciotto, I., Duggan, H. M., Wood, R., Kosnett, M. J., & Smith, M. T. (1992). Cancer risks from arsenic in drinking water. Environmental Health Perspectives, 97, 259-267. https://doi.org/10.1289/ehp.9297259