Toxic Beginnings: 
Cancer Risks to Children from California's 

Air Pollution National Environmental Trust Sep02

Executive Summary

Californians are familiar with the fact that the state has terrible air quality. Over the last thirty years, most attention has focused on the problem of smog and particle (soot) pollution and the innovative policies that have been developed to combat them. But recently, more attention has been paid to what California law calls toxic air contaminants, or "TACS." TACS are chemicals that are emitted into the air from many of the same sources that contribute to smog and soot: vehicles, equipment, and factories. Though many of these chemicals contribute to smog, they also independently contribute to cancer, birth defects, and other health problems.

Toxic Beginnings calculates the cancer risk to children from the measured levels of TACs in the five most populated air basins in California: the San Francisco Bay Area, the San Joaquin Valley, the Sacramento Valley, San Diego, and the South Coast. It updates and broadens an earlier report by the National Environmental Trust on the risk TACs pose to children in the Los Angeles area, and it also includes risk estimates from breathing particles generated by emissions from diesel-powered vehicles.

The state Air Resources Board (ARB) monitors TACs throughout the state and publishes the concentrations found in outdoor air. For cancer-causing TACs, ARB also publishes the estimated cancer risk these concentrations pose to Californians. For example, ARB’s 2002 Almanac of California Emissions and Air Quality demonstrates that the levels of ten cancer causing TACs in the South Coast region (including the estimated levels of diesel exhaust particles) pose a cancer risk 1,005 times the EPA’s lifetime acceptable level.1

While the ARB’s risk estimates are alarming on their own, they actually understate the urgency of the cancer threat because they are calculated over the entire lifetime of an “average” adult. As the state’s own risk assessment agency has noted, the scientific literature is filled with studies demonstrating that exposures to carcinogens early in life result in a greater possibility of getting cancer compared to the same exposures later in life. In other words, children are more susceptible to getting cancer from the pollutants in outdoor air. But children are also more exposed to those pollutants because of their different behavior patterns and their physiology.

Because children breathe more air relative to their body weight, their exposure to air contaminants is higher relative to adults. NET used peer-reviewed and commonly accepted methodology to account for that increased exposure and show how much cancer risk is accumulated early in life. Table 1 shows that a baby born in California will be exposed to such high levels of toxic air contaminants that the child will exceed EPA’s lifetime acceptable exposure level for cancer at a very early age and will exceed the lifetime acceptable exposure level by many multiples by age 18.

Table 1 Summary of Cancer Risk to Children from Air Pollution in Five California Air Basins

		   Time before Infant				Multiple over the	Multiple over the
		   Reaches EPA’s	Multiple over the	One-in-One Million 	One-in-One Million
		   One-in-One Million	One-in-One Million	Limit by Age 18		Limit by Age 18
Region 		   Lifetime Limit       Limit by Age One	(boy)			(girl)
South Coast 	   12 days 		30 			359 			344 
San Francisco Bay  19 days 		19 			229 			220 
San Diego 	   19 days 		19 			224 			214 
Sacramento Valley  23 days 		16 			186 			178 
San Joaquin Valley 21 days 		17 			206 			197

The overwhelming majority of this exposure comes from diesel particulate matter and four chemicals: 1,3-butadiene, benzene, carbon tetrachloride, and formaldehyde. The majority of emissions of these chemicals other than carbon tetrachloride come from “on-road” mobile sources, such as cars and trucks, as well as “other mobile sources” such as farm and construction equipment. The exact mix of sources varies with each region. People who live closer to sources of the ten TACs — such as chrome plating facilities or trucking depots — may receive a higher dose than the regional averages calculated by the ARB, so their cancer risk could be even higher than the estimates in Table 1 suggest.

Cancer risk is assumed to be cumulative across chemicals and over time. For that reason, the potential risk that a child rapidly accumulates in California from simply breathing will not go away when the child is older, even if the air is cleaner when the child reaches adulthood. Remarkably, if the carcinogens in California air were cleaned up to the EPA’s acceptable level immediately, a child born in California would still exceed the lifetime acceptable cancer risk by age four and an adult moving to California would exceed it in seven years. This is because EPA’s acceptable cancer risk level does not take into account children’s greater exposure to air pollution and the cumulative effects of being exposed to several carcinogens at the same time.

These findings, therefore, add new urgency to federal, state, and local efforts to reduce toxic air pollution. They suggest that every opportunity should be taken at all levels of government to reduce cancer-causing air pollution as much as possible. These measures include aggressively enforcing existing rules and permits and making rules now under consideration as stringent as possible. The findings also suggest that policy makers should emphasize the use of alternative technologies and fuels that eliminate or drastically reduce the emission of air toxics, instead of more traditional control measures.

More specific policy recommendations are summarized as follows:

U.S. EPA

• Promulgate a strong mobile source air toxics rule by 2004 and off-road diesel rule (fall 2002). • Enforce the on-road diesel rules and consent decree with diesel engine manufacturers. • Revise the one-in-one million cancer risk goal to reflect the special vulnerability of children and the cumulative effect of exposures to multiple chemicals.

California ARB

• Expedite new standards and control measures for those chemicals that are on the priority list of the Children’s Environmental Protection Act passed in 1999 (SB 25) and add 1,3 butadiene, hexavalent chromium, and carbon tetrachloride to the second tier list. • Improve monitoring, enforcement, and permitting in heavily impacted communities. • Aggressively implement the Diesel Risk Reduction Plan, including an inspection and maintenance program, and accelerate the switch to cleaner technologies.

Local and Regional Governments

• Replace diesel transit fleets (buses and ferries), school bus fleets, and other municipal vehicles with cleaner alternative-fuel vehicles where possible. • Retrofit existing fleets with emissions control equipment, starting with the dirtiest vehicles, where replacement is not possible.

RISK ASSESSMENT PARAMETERS

Risk is essentially a combination of a person’s exposure to a particular substance and the potency of that substance.

a. Exposure

The three parameters that have the greatest influence on exposure are body weight, exposure period, and lifetime. For inhalation exposures, such as those in this report, the average amount of air breathed each day is also important. As stated previously, a standard risk assessment uses a body weight of 70 kilograms, an exposure period of 70 years, and also assumes a 70-year lifetime. The default inhalation rate is 20 cubic meters of air per day, and the default inhalation rate to body weight ratio is 0.286 cubic meters of air per kilogram per day.

For children, however, body weight and inhalation rate change year by year, as shown in Table 5a and 5b12:

Table 5a Body Weight and Inhalation Rate for Male Children

	BODY	INHALATION	INHALATION RATE TO
AGE 	WEIGHT 	RATE 		BODY WEIGHT RATIO
(years)	(kg)	(m3/day) 	(m3/kg-day)
<1 	7.6 	4.5 		0.592
1–2 	13 	6.8 		0.523
3–5 	18 	8.3 		0.461
6–8 	26 	10 		0.385
9-11 	36 	14 		0.389
12–14 	50 	15 		0.300
15–17 	66 	17 		0.258

Table 5b Body Weight and Inhalation Rate for Female Children

	BODY	INHALATION	INHALATION RATE TO
AGE 	WEIGHT 	RATE 		BODY WEIGHT RATIO
(years)	(kg)	(m3/day) 	(m3/kg-day)
<1 	7.6 	4.5 		0.592
1–2 	13 	6.8 		0.523
3–5 	18 	8.3 		0.461
6–8 	26 	10 		0.385
9–11 	36 	13 		0.361
12–14 	49 	12 		0.245
15–17 	56 	12 		0.241

Data in these tables show that infants breathe more than twice the air per unit of body weight as they will at age 18. For male infants the ratio is 2.3, and 2.7 for females.

Inhalation exposure is based on the concentration of the contaminant in the air and calculated as an “average daily dose” (ADD), which takes the person’s physical characteristics into account, the length of the exposure, and the person’s lifetime13:

ADD = (C x IR x ED) / (BW x AT x 1000), where ADD = average daily dose (mg/kg-day); C = contaminant concentration in the inhaled air (mg/m3); I R = inhalation rate (m3/day); ED = exposure duration, or the total time a person is exposed to the pollutant (days); BW = body weight (kg); and AT = averaging time (days), equal to 70 years for cancer risk assessment, or 25,550 days.

This report uses the data in Tables 5a and 5b, along with the concentrations in Table 4 to calculate an ADD for each year from birth through age 18 for males and females.

b. Chemical Potency

In general, models for assessing carcinogenic (or cancer-causing) effects assume that at low doses there is a simple, straight-line (or linear) relationship between exposure and the potential risk of getting cancer. That is, the greater the exposure, the greater the potential risk. The carcinogenic effects models take data on dose and response available from animal or human studies and synthesize them into that linear relationship. Each cancer-causing chemical fits into some sort of straight line, and each of these lines has a different slope. The slope of the line is called the “slope factor” and represents the increase in risk with increase in exposure. Slope factors in this report come from the California Environmental Protection Agency and are listed in ARB’s 2002 California Almanac of Emissions and Air Quality.

EXPRESSING CANCER RISKS

Since cancer risk is assumed to accumulate over a lifetime, risks resulting from different exposures can be added together within that lifetime. Thus, the potential risk calculated for an infant from birth through his or her first birthday can be added to the potential risk calculated for year two, etc., to calculate potential risk for a child’s first 18 years. This addition is appropriate since the exposure is assumed to be continuous through breathing air containing a particular concentration of pollutants.

As standard practice, risks are calculated for exposures to individual chemicals. As long as cancer risk is being calculated, the cancer risk from exposure to one chemical is typically added to the cancer risk from exposure to another chemical to get a total potential cancer risk.14 The actual potential cancer risk from the two chemicals may be less than, greater than, or equal to the result of adding risks in this manner. The various chemicals may act independently, may cancel out certain effects in each other, or could even work in concert to produce effects greater than the sum of the individual effects. Data on interactions are extremely limited, and so in the absence of better information, cancer risks in this report are added across chemicals.

Since cancer risks are a probability, they are typically expressed in terms of some number-in-one million (such as one-in-one million or two-in-one million). Numerically, this probability is expressed as the number times ten to the minus sixth power (number x 10-6).

As stated previously, U.S. EPA considers potential risks greater than 1 x 10-6 to be worthy of further investigation, and the Clean Air Act sets this same risk level as its goal for reduction in hazardous air pollutant concentrations in the environment.

ENDNOTES

1 http://www.arb.ca.gov/aqd/almanac/almanac02/almanac02.htm .

2 OEHHA, Prioritization of Toxic Air Contaminants Under Children’s Environmental Protection Act, Final, October 2001, p. 21.

3 http://www.epa.gov/children/indicators/childhood_cancer.html .

4 OEHHA, ibid., p. 25.

5 http://www.arb.ca.gov/aqd/toxics/toxics.html .

6 As shown in the methodology section, the inhalation to-body-weight ratio for girls drops more quickly than for boys beginning at age nine, since girls mature more quickly. Consequently, from birth to age 18, girls accumulate approximately five percent less risk than boys by these calculations.

7 While it is standard risk assessment practice to add the risks together, the actual potential risk could be greater or less than the sum of the individual risks for the 10 chemicals. See the methodology section for a discussion of summing potential risks from different chemicals.

8 OEHHA, ibid., p. 28.

9 California Air Resources Board, “Risk Reduction Plan to Reduce Particulate Matter Emissions from Diesel-Fueled Engines and Vehicles,” October 2000.

10 Natural Resources Defense Council and Coalition for Clean Air, No Breathing in the Aisles, January 2001.

11 ARB provides a summary of monitors located in each air basin in the 2002 California Almanac of Emissions and Air Quality (http://www.arb.ca.gov/aqd/almanac/almanac02/almanac02.htm). TAC concentration data for 1999, 2000, and 2001 are available at http://www.arb.ca.gov/aqd/toxics/sitesubstance.html.

12 U.S. Environmental Protection Agency. Exposure Factors Handbook, Volume 1, General Exposures. EPA/600/ P-95/002Fa, August 1997. Body weights from Table 5–10, daily inhalation rates from Table 5–11.

13 Cancer risks are assumed to be chronic and accumulate over a lifetime. Thus, even if a person is exposed to a particular contaminant for one year, and then is not exposed to that particular chemical again, the cancer risk is spread over the person’s lifetime, generally assumed to be 70 years.

14 This addition is typically done even though exposure to each chemical may not produce the same form of cancer in an individual. The result is a total potential risk of cancer in general, rather than a specific form of cancer.

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