realistic biological and exposure/dose relationships: how they modify perceived human health &...

Realistic Biological and Exposure/Dose Relationships: How They Modify Perceived Human Health & Ecological

RiskMay 22, 2008

Allen S. Lefohn, Ph.D.

A.S.L. & Associates

Helena, Montana

asl-associates.com

Discussion Subjects

• Policy Relevant Background (PRB);• Effect of PRB on Epidemiological Risk;• Disproportional Reduction in Concentrations as

Emission Reductions Implemented;• Empirical Evidence for Changes in Distributions

of Hourly Average Concentrations by Month (i.e., Rollback);

• Evidence for Nonlinearity in Human Health Dose-Response; and

• Evidence for Nonlinearity in Vegetation Exposure- and Dose-Response.

Policy-Relevant Background• EPA has defined Policy-Relevant

Background (PRB) as those concentrations that would result in the United States in the absence of anthropogenic emissions in continental North America (EPA CD, 2006).

• Policy Relevant Background concentrations include contributions from natural sources everywhere in the world and from anthropogenic sources outside of North America.

Estimation of Background Ozone is Very Important for Getting the

Risk Estimates Correctly

One of the key inputs into the risk analyses is the range of background ozone concentrations. If EPA underestimates background ozone, then the Agency overestimates sickness and premature deaths.

If Actual Background Ozone is Higher, Then Predicted Effects

Are Lower

Background Ozone Higher Than Predicted by EPA

Decrease Predictions ofSickness and

Premature Deaths

=

Why is PRB Important?

• The PRB concentrations define the level below which O3 standards cannot be set.

• Correctly estimating PRB is very important because inadequate characterization may lead to levels that are too low, resulting in 1) inflated human health risk estimates and 2) overly optimistic policy expectations on the levels to which hourly average O3 concentrations can be lowered as a result of emission reduction requirements.

Background Ozone Levels of Air Entering the West Coast of the

U.S. And Assessment of Longer-Term Changes

Samuel J. Oltmans, Allen S. Lefohn, and Douglas Shadwick

asl-associates.com

Atmospheric Environment (2008). In Press

Identification of Sites

Observations Trinidad Head, CA

• An analysis of surface ozone measurements at a west coast site in northern California (Trinidad Head) demonstrates that this location is well situated to sample air entering the west coast of the U.S. from the Pacific Ocean.

• During the seasonal maximum in the spring, this location regularly observes hourly average ozone mixing ratios 50 ppb in air that is uninfluenced by the North American continent. Mean daytime values in the spring exceed 40 ppb.

Back trajectories to Trinidad Head for all days in April 2002-2005 on which there was an hourly average ozone concentration 50 ppb (upper panel) and for April 2003 (lower panel).

2003 January 739 0.008 0.014 0.021 0.028 0.034 0.038 0.041 0.044 0.046 0 0.000 0.312 2003 February 660 0.014 0.023 0.029 0.034 0.038 0.044 0.045 0.048 0.050 1 0.000 0.587 2003 March 713 0.012 0.028 0.034 0.038 0.042 0.047 0.049 0.051 0.052 23 0.000 1.076 2003 April 720 0.023 0.036 0.042 0.046 0.048 0.052 0.054 0.058 0.064 187 0.310 2.722 2003 May 743 0.011 0.029 0.036 0.041 0.045 0.050 0.052 0.054 0.057 96 0.000 1.773 2003 June 720 0.016 0.025 0.032 0.037 0.040 0.044 0.046 0.053 0.054 13 0.000 0.816 2003 July 744 0.003 0.015 0.020 0.023 0.026 0.031 0.032 0.036 0.041 0 0.000 0.109 2003 August 740 0.007 0.020 0.024 0.027 0.030 0.034 0.035 0.038 0.041 0 0.000 0.185 2003 September 720 0.006 0.016 0.025 0.030 0.035 0.040 0.042 0.054 0.060 13 0.120 0.507 2003 October 743 0.004 0.016 0.025 0.028 0.033 0.038 0.040 0.044 0.047 0 0.000 0.300 2003 November 696 0.006 0.023 0.028 0.032 0.035 0.039 0.041 0.046 0.047 0 0.000 0.396 2003 December 725 0.004 0.024 0.029 0.033 0.037 0.041 0.042 0.045 0.050 1 0.000 0.492

Trinidad Head, CA

CharacterizationYear Month Num. Obs Min P10 P30 P50 P70 P90 P95 P99 Max N50

Channel Islands National Park, CA

Observations Channel Islands National Park, CA

• A location in southern California (Channel Islands National Park) demonstrates many of the same characteristics during the spring as Trinidad Head in terms of air flow patterns and ozone amounts suggesting that background levels of ozone entering southern California from the Pacific Ocean are similar to those in northern California.

The Effect of Getting Background Ozone Incorrect

• Modifying EPA’s estimated ozone background levels (mostly in the 15 to 25 ppb range) by 5 ppb for Los Angeles would make the risk by as much as 86% lower in the estimates for non-accidental mortality;

• If the Agency had used background ozone data, which shows observed actual background ozone at Trinidad Head (CA) at levels as much as 20 ppb higher than modeled background, the 86% reduction for non-accidental mortality would have been even greater.

Comparison of ozone-related non-accidental mortality incidences “74/4” when PRB estimates are increased 5 ppb – 2002 air quality data.

The Rate of Decline of Ozone Concentrations

Empirical Rollback

Lefohn et al. (1998) identified those sites that demonstrated a significant reduction in ozone levels for the period 1980-1995. Using the data from the sites that experienced reduced ozone levels over the period of time, we investigated whether the rate of decline of the mid-level hourly average concentrations was similar to the rate experienced by the high hourly average concentrations.

Greater Resistance to Reducing the Mid Range of Concentrations

• The higher hourly average concentrations (i.e., above 90 ppb) decreased at a faster rate (greater negative rate per year) than the hourly average concentrations in the mid-level range.

• For many sites, the number of hourly average concentrations at the low end of the distribution also decreased.

• Both the high and low ends of the distribution were moving toward the center of the distribution.

Changes in O3 Reduction Rate

10.000

8.000

6.000

4.000

2.000

0.000

2.000

4.000

0.001-0.010

0.011-0.020

0.021-0.030

0.031-0.040

0.041-0.050

0.051-0.060

0.061-0.070

0.071-0.080

0.081-0.090

0.091-0.100

0.101-0.110

Ventura Co., CA Cook Co., IL Bristol Co., MA Boone Co., KY

Changes in the Distribution of HourlyAverage Concentrations Over Time

Concentration Range (ppm)

Med

ian

Rel

ativ

e D

iffe

renc

e A

s P

erce

nt P

er Y

ear

Changes in O3 Reduction Rate

Distribution of changes by month for a monitoring site located in Fairfield County, Connecticut (AQS 090013007) for the period 1990-2005 for the months with significant changes.

Changes in O3 Over Time4th Highest 8-Hour

Daily Maximum Concentration by YearFairfield County, CTAQS ID 090013007

1980-2007

0.000

0.050

0.100

0.150

0.200

0.250

19

80

19

82

19

84

19

86

19

88

19

90

19

92

19

94

19

96

19

98

20

00

20

02

20

04

20

06

Year

Co

nc

en

tra

tio

n (

pp

m)

Nonlinearity in Dose-Response• There is sufficient evidence from the controlled

human health laboratory experiments of the existence of a nonlinear exposure response relationship.

• The results published by Hazucha et al. (1992) and Adams (2003, 2006a, 2006b) suggest that the higher hourly average concentrations elicit a greater effect than the lower hourly average values in a nonlinear manner and that identical 8-hour average concentrations with different combinations of hourly values will result in different FEV1 responses (Hazucha and Lefohn, 2007).

Exposure-Response Curve Used to Assess Effects on School Age Children

Concentration-response function for lung function decrements.Source: Modified from U.S. EPA (2007).

Nonlinearity in Dose-ResponseSummary

Nonlinearity means that the use of 8-hour exposure metrics will provide highly uncertain risk estimates when controlled human laboratory experimental results are used in the modeling exercises.

Human Laboratory Results

• Research results published by Professor Bill Adams formed the basis for these data points;

• Adams (2002) and Adams (2006) reported no statistically significant effects for lung function decrements at either the 0.04 ppm or 0.06 ppm levels; and

A CASAC’s Member’s ConcernAt least one member of CASAC’s Ozone Panel felt uncomfortable using the data points at the 0.06 and 0.04 ppm levels (Henderson, 2007b) to set base policy. The member stated

... other cases, such as the specific case of 0.060 or 0.040ppm exposures (Adams 2006), this approach amounts to attempting to find effects in a very few individuals when the statistical tests are not significant, which is a dangerous precedent – especially in this case where we are looking at small effects in 3 of 30 vs. 1 of 30, a pitiful number on which to attempt to base policy...

Nonlinearity in Dose-ResponseEpidemiology

The EPA’s focus on the existence of a threshold and at what level (e.g., near the lower limit of ambient O3 concentrations in the United States), obfuscates the more important observation that there is ample evidence for nonlinearity in the concentration-response function.

Strong evidence exists to show that nonlinearity in the concentration-response function exists (reported results showing seasonal differences and risk differences applying exposure indices with different concentration cutoffs).

Nonlinearity in Dose-Response

• It is important to stress that a nonlinear concentration-response relationship does not imply the existence of a “threshold”.

• A nonlinear concentration-response relationship can exist without a threshold.

NRC ReportThreshold

“The association between short-term variations in ambient ozone concentrations and fluctuations in mortality rates is usually characterized as linear. Because the association is based on epidemiologic studies that can only approximate exposure on the basis of ambient monitoring data, the assumption of linearity should be viewed with caution.”

Estimating Mortality Risk Reduction and Economic Benefits from Controlling Ozone Air Pollution - NRC (2008)

NRC Report Choice of Exposure Metrics

• “The choice of averaging period to characterize short-term ozone exposure in linking ambient ozone concentration with mortality risk can have a large effect on estimates….”


NRC Report Choice of Exposure Metrics

• “Together, low personal exposures and weak personal-ambient relationships suggest that 24-h ambient ozone concentrations are poor proxies for personal exposure.”

• “Future studies of the effects of short-term ozone exposure should determine whether and how much daily peak exposures, such as 1-h or 8-h exposures, and longer-term average exposures, such as over 24 h, are associated with ozone-related mortality.”


Summary The PM Staff Paper (EPA, 2005) noted

that a large degree of uncertainty in the human health risk assessments, using results from epidemiological studies, occurred when proportional and nonlinear concentration-response functions were applied in the Agency’s risk analyses.

Based on rollback, PRB, and nonlinearity considerations, there is considerable uncertainty associated with estimates of health risk whose basis is linked to epidemiological models.

Nonlinearity in Dose-ResponseVegetation

Musselman, R.C., R.J. Oshima and R.E. Gallavan. (1983) J. Amer. Soc. Hort. Sci. 108(2):347-351.


• There is sufficient evidence from the controlled and uncontrolled vegetation experiments that a nonlinear exposure- and dose-response relationship exists.

• The results summarized by EPA (2006) and the critical review by Musselman et al. (2006) indicate that the higher hourly average concentrations elicit a greater effect than the lower hourly average values in a nonlinear manner.


• The cumulative exposure W126 exposure index uses a sigmoidally weighted function as described by Lefohn and Runeckles (1987) and Lefohn et al. (1988).

• The W126 index focuses on the higher hourly average concentrations, while retaining the mid- and lower-level values and avoids applying a non-biologically based artificial threshold.

The form of the sigmoidal weighting function used in the W126 exposure index. Source: Lefohn et al. (1988).

Shortcomings of Exposure Index• Under experimental conditions, the same exposure

index values result in different yield when exposure regimes, some containing peaks and some without peaks, are used;

• The cumulative exposure indices are unstable for use in protecting vegetation because peak concentrations were present in the experiments used to determine the vegetation exposure-response relationships; and

• The use of an ambient W126 exposure index to predict impact to vegetation is inadequate unless the frequency of elevated hourly average concentrations (i.e., 0.10 ppm) is included in the estimate of effects

Overestimating Vegetation Effects

Estimated black cherry annual biomass loss based on interpolated 2001 maximum 3-month 12-hour W126 with a 10% downward adjustment of hourly O3 concentrations. Source: Appendix to Staff Paper (U.S. EPA, 2007).

Allegheny National Forest• Morin et al. (2006) reported on the O3

bioindicator survey results conducted for the Allegheny National Forest for the period 1998 and 2001 for both black cherry and pin cherry for each year; and

• The authors concluded that none of the forest health indicators revealed reason for concern for the health of the population of black cherry in the Allegheny National Forest.

Reasons for Overestimates• During the last 25 years, most approaches used for

studying O3 effects on plant growth and development have employed either simulations of the diurnal ambient O3 profile or enhancement/reduction of the ambient O3 concentrations;

• Many research investigations apply the NCLAN experimental fumigation protocols;

• The O3 exposure patterns used in the open-top chambers in many of the vegetation experiments included numerous occurrences of hourly average concentrations 0.10 ppm (U.S. EPA, 1996b).

Solution to the Problem

• The W126 exposure metric needs to be combined with the number of hourly average concentrations 0.10 ppm in order to take into consideration the experimental fumigation protocols used;

• The Palmer Drought Index or a similar index is required to take into consideration the soil moisture conditions; and

• Combining the W126, the number of hourly average concentrations 0.10 ppm, and the Palmer Drought Index has been shown to improve the relationship between exposure and vegetation effects.

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