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Understanding Hazard Identification and Risk Assessment in Relation to Air Pollution

Hazard Identification and Risk Assessment in Relation to Automobile Emissions

The first thing to do is look at the risk curve for this problem. The Y-axis (the vertical axis) indicates fatalities per year (0.00002345 to 0.1737), while the X-axis (the horizontal axis) indicates the number of years (from 1 to 40). Looking at the curve, it can be seen that there is an increased probability of deaths in any given year the closer the number of years is to 40.

(i) The probability of more than 100 fatalities in a given year as a result of an accident;

To determine this, use Figure 1 along with P(X > 100). Below are Figure 1 and P(X > 100):

P(X > 100) = 0.0592156799

Figure 2 shows that when X = 40, then P(X > 100) = 0.0592

Hence, P(X > 100) = 0.0592 for a given year as a result of an accident after 40 years.

(ii) If the risk curve in Figure 1 were to apply to each of the 30 nuclear power reactors in the United States, what is the probability of 20 or more fatalities resulting from accidents during the 40-year operating life of the reactors?

To solve this problem, first use Figure 1 and P(20 < X < 30) and figure out what year it would be where there is a probability of 20 fatalities per year. Below are Figure 1 and P(20 < X <30):

P(20<X<30)=0.0026018472

Figure 3 shows that it would be at 34.

Since there are 30 nuclear power reactors in the United States, use P(X > 20) and P(20 < X < 30) as follows:

P(X > 20) = 0.4504

P(20 < X < 30)=0.0026+0.4504=0.4530

Thus, there is a 45.3% chance of accidents leading to more than 20 fatalities after 40 years of operation for all U.S. nuclear power reactors put together: 30 x 0.4530 = 13.65%. So, there's about a 14% chance of accidents resulting in more than 20 during the 40-year operating life of all U.S. nuclear power reactors put together.

Automobile emissions may pose a health hazard to the surrounding communities. Various gases, such as carbon monoxide (CO), nitrogen oxides (NOx), and volatile organic compounds (VOCs), are released from automobile exhaust. Pollutant concentrations near busy roads can be pretty high. The time-weighted-average of pollutant concentration at the residential area is estimated to be about three µg/m3 for CO and two µg/m3 for NOx. These values exceed EPA's national ambient air quality standard by 50 times and 100 times for CO and NOx, respectively. There is evidence that children who live close to major roads have higher developmental abnormalities such as neural tube defects and low birth weight.

Hazard Identification and Risk Assessment in Relation to Petroleum Refineries

Petroleum refinery is a significant source of air pollutants. The release of various types and amounts of pollutants depends on the refinery's location, capacity, and amount and type of petroleum processed. For example, Chevron's Richmond Refinery located in California emits hydrogen sulfide (H2S), carbon monoxide (CO), nitrogen oxides (NOx), volatile organic compounds (VOCs), and particulates such as PM 10, lead, manganese, chromium, arsenic, selenium and dioxins/furans.

Sanitary landfill is another primary source of air pollution because it releases methane gas from decomposition. Methane concentration inside an enclosed structure such as a building can be pretty high. For example, the methane concentration in the air at the landfill is about 970,000 µg/m3, while inside an enclosed structure, it is about 930,000 µg/m3.

According to the EPA's Integrated Risk Information System (IRIS), 1 out of 50 individuals has asthma. If 1000 people are exposed to 100 ppm CO for 8 hours, there will be one extra case of asthma. When only adults are considered, the risk increases to 1 extra case per 20 persons or a 5% increase compared to a clean air environment. According to IRIS, for NOx and VOCs, their carcinogenic potentials are low with no threshold effect. It means that any exposure to NOx or VOCs is considered harmful.

Hazard identification is the process of identifying which hazardous materials are present in a given environment, what chemical and physical properties they have, how people might be exposed to these substances, their toxicological properties. Exposure assessment measures the quantity of actual contact with hazardous material by individuals in an at-risk area.

Consequence assessment assesses the number of people at risk and the degree of damage caused by each pathway (i.e., air pollution) [8]. A mathematical model may be used to estimate population and possible health effects resulting from exposure to air pollutants such as SO2 and PM10. Risk management includes various strategies such as source control, exposure control, and public education.

Hazard assessment aims to analyze the possible hazards caused by a potential environmental disaster. For example, a chemical leak would pose a health risk for people nearby but no environmental harm. The hazardous materials may be classified into different types based on their source and release: radiation, airborne toxins, chemical, biological, etc. Hazardous material can also be classified according to how it might enter the body: inhalation, ingestion, or absorption through the skin. In addition to specific information about the hazardous material itself (i.e., toxicity), its consequences should also be considered. For example, even if a hazardous substance has low toxicity in general, an accident during transportation could release a large amount of it and cause harm.

Hazard Identification and Risk Assessment in Relation to Sanitary Landfills

A hazard also includes the amount of contact and length of exposure to a substance. According to EPA's Community Right-to-Know Laws, there are four major types of chemical hazards: explosive power, flammability, health hazards (i.e., carcinogens), and reactivity. Reactivity describes hazardous characteristics which result from how matter changes when it contacts other substances or forms under certain conditions such as heat or pressure. The consequences of exposure may affect individual organ systems, including the blood system, digestive system, respiratory system, etc., or multiple organ systems, including the central nervous system, etc. Therefore, the risk assessment should consider all possible effects of chemical release on people near the accident site for both short term (acute effects) and long term (chronic effects).

Hazard identification is the first step in risk assessment. It involves identifying which hazardous material is present in a given environment, its chemical properties, how it may enter into people's bodies, and the degree of harm it causes when entering into the human system. Factors that affect the toxicity of the substance include the amount one person can take at once, the duration of exposure before symptoms appear, whether ingestion or inhalation is the dominant means by which people are exposed to the substance, etc. Even if a material has low toxicity when considering general cases, an accident during transportation could release a large amount of it and cause harm. For example, hydrofluoric acid released in the air can severely damage the lungs and bones. Ingestion of the acid may cause severe damage to internal organs such as the heart, liver, kidneys, etc.

To properly assess if a material is hazardous, people need to know how long it takes for symptoms like difficulty breathing or vomiting to appear after contact with the substance. Symptoms also depend on whether the substance penetrates the skin and what amount can enter the human body at once. For example, contact with benzene causes nausea and vomiting within minutes due to its high toxicity. Thus, benzene can quickly enter people's systems through inhalation and ingestion. However, safe levels of benzene in the air are much lower than those which would harm people's health even if they do not inhale it.

Exposure assessment can be a challenging part of risk assessment because it attempts to predict the magnitude and frequency of human contact with the hazardous material. The first step in exposure assessment is to determine how many people might contact the hazardous material where and when it could happen, such as during transportation, accidental leak, etc. Then one has to decide who might be exposed by considering population characteristics such as age group, sex, race, lifestyle (i.e., smokers), etc. Finally, one needs information about the duration and intensity at which each person would be exposed. For example, workers should wear respiratory protection if a chemical tanker truck crashes and releases hydrofluoric acid vapors, which damages lungs and bones upon inhalation at a near point source. However, workers could face less risk if hydrofluoric acid is released into the air at a faraway point source.

Factors Affecting the Toxicity of Hazardous Materials

Exposure assessment can use statistical data to predict how many people might be affected in a given area over time. Exposure assessment should consider the worst-case scenario where all persons are potentially exposed at the highest-level intensity for their entire exposure period, which would result in a significantly large number of people being affected. The smaller the area and the shorter the duration of exposure, the lesser people would be hurt by it. For example, accidental leakage of gasoline from a tanker truck could lead to thousands of people inhaling gasoline vapor, which causes headaches and nausea within minutes to hours depending on the high concentration near the accident site. On the other hand, accidental gasoline leaks in a waterway can be less harmful to people due to lesser concentrations in the air near the accident site and relatively long duration of exposure in water compared to air.

Consequence assessment is another step after exposure assessment in risk assessment. It is about predicting how many people might be sick or dead if exposed to a specific level of hazardous material for a particular duration of time at maximum intensity. For example, one could estimate how many workers might be affected by inhalation toxicity if they are exposed once during their workday for five minutes at the lowest-level intensity where symptoms appear hours later. If toxic vapors with benzene concentration were released into the workplace environment at point source immediately causing feelings of nausea and headache, workers might wear respiratory protection masks; however, if benzene vapor were released into the workplace environment at a faraway point source gradually over time. They inhaled the vapors for several hours a day during the workweek without respiratory protection; they might face less risk.

Consequence assessment is challenging because it requires statistical data to consider population characteristics, age group, and sex. It uses mathematical tools to estimate how many people might be affected in a given area over time. For example, one could use a mathematical model like "DALY" (Disability Adjusted Life Year), which measures the number of healthy life years lost due to illness or injury from any cause. DALY is a tool used to evaluate the overall health status and compare disease burden among different diseases or health conditions. For example, suppose benzene vapor with a concentration of 0.04 parts per million (ppm) were released into the workplace environment for 5 minutes, after which workers became nauseated within 2 hours. In that case, DALY could be used to estimate how many sick days would be lost due to this exposure. If workers lost ten days at work during one year due to exposure, then the consequence assessment score could be estimated as 10/365*5 =2%.

Exposure Assessment in Risk Assessment

Risk management is about determining what should be done to protect public health once criteria for a specific level of hazardous material are known through hazard identification, exposure assessment, and consequence assessment. Risk management can be challenging since it requires making tough management decisions to protect public health once the criteria for a specific level of hazardous material are known through hazard identification, exposure assessment, and consequence assessment. For example, there needs to be a trade-off between the economic impacts of shutting down a refinery plant due to the release of petroleum hydrocarbon vapors versus protecting human health from hazardous air pollutants emitted from the refinery plant. Another example is that risk management should consider zero level as the threshold for a pollutant because just a few parts per million or micrograms over background levels might result in noticeable symptoms after a long exposure period. For benzene vapor, one could estimate how many people exposed chronically at two parts per million for several years might develop leukemia or other cancers. With this information, risk management would need to determine the acceptable concentration level for gasoline refinery plants considering chronic exposure rate, number of people exposed at the site, and type of cancer that benzene vapor might cause.

The body weights of the workers are 70 kg. The inhalation rates are one cubic meter per hour. Workers are exposed to chemicals for 8 hours a day, 240 days a year for 25 years. The expected life span of an adult is 75 years.

Calculations:

Chronic daily intake in mg/kg/day considering carcinogenicity effects:

Reference dose = 2

Slope factor = 0.5 [mg/kg/day]

Chronic daily intake in mg/kg/day considering carcinogenicity effects:

= Reference dose * Slope factor

= 2 * 0.5 = 1

Chronic daily intake in mg/kg/day assuming carcinogenicity effect is that of reference dose:

= chronic daily intake in mg/kg/day / 70 kg / (80 µg / m3 * 1 m3 / h * 8 hr * 25 yr)

= [Reference dose] [1] [Species used for calculation] [Time unit converted from hours to years] [Species used for calculation][Exposure time period][1]

Calculations: Hazard quotient carcinogenicity

Hazard quotient carcinogenesis = Chronic daily intake in mg/kg/day considering carcinogenicity effects / Reference dose

Hazard quotient carcinogenicity

= 1 / 2

Hazard quotient carcinogenicity = 0.5 Hazard quotient non-carcinogenicity

Hazard quotient non-carcinogenesis = Chronic daily intake in mg/kg/day considering non-carcinogenicity effects / Reference dose

Hazard quotient non-carcinogenicity

Conclusion

= 1 / 2 Hazard quotients are the same. Hazard quotients are below the hazard threshold. Therefore, worker exposure to chemicals is not dangerous regarding adverse health effects.

Reference dose = 2

Slope factor = 0.5 [mg/kg/day]

Hazard quotient carcinogenesis

= Chronic daily intake in mg/kg/day considering carcinogenicity effects / Reference dose

= 1 / 2 Hazard quotients are the same. Hazard quotients are below the hazard threshold. Therefore, worker exposure to chemicals is not dangerous regarding adverse health effects.

The three contaminants are evaluated to have various effect levels. Lead is considered to have a very high effect level of 10 mg/kg/day. Sb has a known carcinogenic effect level of 0.5 mg/l, and the rest is non-carcinogenic. V is considered to have no significant environmental effects at 100 mg/kg and greater than 1000 mg/kg, respectively (ATSDR, 1993).

There are quite a large number of areas with high lead concentrations. In this case study, it turns out that the area where the brownfield site lies is under scrutiny for soil contamination due to its proximity to several other sites nearby, which has required extensive cleanup efforts up until now. The current task was to assess whether further action needed to be taken.The site is not the worst but still outside of a reasonable safety level. To determine whether further action should be taken, first, the actual risk assessment needs to be performed as shown in equation one below:

pH = Pb + Sb/2 + V/24 .

In this case, study, consider that a child of 10 kg body weight will ingest on average 200 mg/day of soil. The ingestion rate was determined by considering a normal play behavior and multiplying it with an assumed 50% contamination factor due to weathering processes generally increasing the concentration of contaminants over time. Applying equation one leads to figure 2, where one can see that even though three contaminants were found at high concentrations in the soil, the total ingestion is well under the maximum effect level for all three contaminants.

Since this case study looks like no further action needs to be taken to reduce the risk of exposure by ingestion, another option was considered, which led to Figure 3 below. As seen from this figure, if Pb were removed entirely and only V and Sb were left in, then according to equation one above, the resulting ingestion would be close to or even exceed that of when nothing gets done at all. It means that Pb should be remediated. The effect levels for Vanadium (V) and antimony (Sb) are already deficient compared to higher concentrations usually required for remediation. Also, the resulting ingestion will not exceed when nothing gets done, which is another argument for taking action even though it may be only Pb alone.

The results conclude that some additional action must be taken to reduce the risk of exposure by ingestion for this case study. It turns out that children are most affected by soil ingestion because of their play behavior at early stages in life, where they tend to ingest more significant amounts of soil compared to adults. Therefore the primary focus should probably be on remediation of Pb contamination. Considering that V and Sb are factors while performing an overall risk assessment, dealing with all three contaminants might make more sense.

Pb should be remediated by removing 500 mg/kg of contaminated soil. The results obtained above are based on the following assumptions:

• Site use is planned for housing in the future.
• A child of 10 kg body weight will ingest on average 200 mg/day of soil.
• Normal play behavior assumptions were used to determine ingestion rate.
• 50% contamination factor due to weathering processes was assumed.
• Remediation efforts need to be economically feasible and technically sound.

In reality, many factors may differ from those stated here, which can lead to different conclusions or additional factors that need to be considered.

A decision tool should be developed to perform a risk assessment similar to what has been done for this case study. It will help stakeholders decide whether or not further action needs to be taken to reduce the risk of exposure to non-carcinogenic contaminants. The aim is that the tool will be simple and easy to use but still very accurate.

The chemical concentrations, lifetime risk, and hazard indices for a person inhaling all three chemicals are as follows:

Benzene: Exposure concentration = 30 µg/m3

Individual risk = 0.5 × 10-5/30 = 6.25*10-7 (per µg/m3) or 625×10-7 (per 30 µg/m3)

Excess cancer risk in the community = 40×625=allowable concentration of 200 µg/m3

Cadmium: Exposure concentration = 40 µg/m3

Individual risk = 0.5 × 10-4/40 = 2.5×10-6 (per µg/m3) or 2.5×10-7 (per 40 µg/m3)

Excess cancer risk in the community = 50×2.5=allowable concentration of 125 µg/m3

Arsenic: Exposure concentration = 50 µg/m3

Individual risk = 0.5 × 10-5/50 = 1.25×10-7 (per µg/m3) or 1.25×10-7 (per 50 µg/m3)

Excess cancer risk in the community = 30×1.25=allowable concentration of 38 µg/m3

Hazard indices for benzene, cadmium and arsenic are:

Benzene: HA = 625/30 = 20 (per µg/m3) or 200 (per 30 µg/m3)

Cadmium: HA = 2.5/40 = 0.0625 or 6.25×10-4 (per µg/m3)

Arsenic: HA= 1.25/50 = 0.025 or 2.5×10-4 (per µg/m3)

The total hazard index for a person inhaling all three chemicals is as follows:

HA = 20 + 6.25×10-4 + 2.5×10-4 = 8.75×10-6 or 0.0875 (per µg/m3) or 8.75 (per 10 µg/m3)

Life-time individual risk for a person inhaling all three chemicals = (0.5×10-5) × (8.75×10-6) = (4.375/106)=4.37×104

Excess cancer risk in the community = HA × Life-time individual risk= 8.75×10-6×4.37×104 = 0.42 cancer cases (per year).

The chemical intake rate was calculated, and associated risks to each group in the community were determined. Excess cancer risk in the community due to ingestion of drinking water was also determined.

For adults, the chemical intake rate is:

Intake Rate = [(Water Consumption) / (Food Conversion Efficiency)] x Chemical Concentration in Food

Intake Rate = [(64 L) / (0.8)] x Chemical Concentration in Food

Intake Rate = 96 L/d x Chemical Concentration in Food

Intake Rate = 96 mg/d for adults

For children, the chemical intake rate is:

Intake Rate = [(Water Consumption) / (Food Conversion Efficiency)] x Chemical Concentration in Food

Intake Rate = [(20 L) / (1.2)] x Chemical Concentration in Food

Intake Rate = 32 L/d x Chemical Concentration in Food

Intake Rate = 32 mg/d for children

The cancer risk was calculated using the following equation, where C is the chemical concentration in drinking water (in mg/L), BW is body weight (in kg), and EF is exposure frequency (in d/yr):

Risk = [(C x BW) / (EF x 365 days)] x 10-6

Benzene: Risk = [(0.03 x 70) / (365)] x 10-6

Risk = 0.00012 x 10-6

Risk/year = 12 chances in 100,000 that the benzene concentration will cause cancer over a lifetime of exposure

Arsenic: Risk = [(0.1 x 70) / (365)] x 10-6

Risk = 0.0072 x 10-6

Risk/year = 72 chances in 100,000 that arsenic concentration will cause cancer over a lifetime of exposure

Cadmium: Risk = [(0.2 x 70) / (365)] x 10-6

Risk = 0.0144 x 10-6

Risk/year = 144 chances in 100,000 that cadmium concentration will cause cancer over a lifetime of exposure

The excess cancer risk is the sum of all three chemicals calculated for adults and children:

Excess Cancer Risk = [(12) + (72) + (144)]

Excess Cancer Risk = 236 chances in 100,000 that the chemical concentrations will cause cancer over a lifetime of exposure

The daily intake for all three chemicals was also calculated using the following equation:

Intake = [(C x BW) / EF] x 365 days

For adults: Intake = [(96 x 70) / 365] x 365 days