Human Exposure Pathways - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 510

For an adult resident, US EPA ( 2004b ) recommended default soil adherence
factors of 0.01 and 0.07 mg/cm 2 for central tendency estimates and reasonable max-
imum exposure cases, respectively. The central tendency value is a geometric mean
derived from a study of groundskeepers, and the reasonable maximum exposure
value is a geometric mean derived for gardeners.
As summarized in US EPA ( 2004b ), geometric mean adherence factors
developed for pipe layers working in dry soil, construction workers, heavy equip-
ment operators, utility workers, and pipe layers working in wet soil are 0.07, 0.1,
0.2, 0.2, and 0.6 mg/cm 2 , respectively (US EPA 2004b ). For typical adult com-
mercial/industrial workers, US EPA ( 2004b ) recommended default soil adherence
factors of 0.02 and 0.2 mg/cm 2 for central tendency estimates and reasonable
maximum exposure cases, respectively. The central tendency value is a geometric
mean derived for commercial groundskeepers, and the reasonable maximum expo-
sure value is a geometric mean derived for heavy equipment operators and utility
workers.
US EPA ( 2004b ) recommended that dermal exposure to sediments be evaluated
in a manner similar to dermal exposure to soils, with two modifications to account
for differences between the two media. First, primarily sediments that are exposed
(i.e., not underwater) for at least a portion of the year should be evaluated, because
sediments covered by water are likely to be washed off the skin before the individ-
ual reaches shore. Second, sediment sample results must be adjusted to reflect wet
weight so they are consistent with the reporting methods of soil adherence studies.
Wet soil sticks to the skin more easily than dry soil, so adherence factors for wet
soil are higher than for dry soil. Geometric mean adherence factors developed for
children playing in wet soil, pipe layers working in wet soil, and reed gatherers are
0.2, 0.6, and 0.3 mg/cm 2 , respectively (US EPA 2004b ).
Shoaf et al. ( 2005a , b ) investigated sediment adherence for adults clamming and
children playing in tide flats. Weighted median and 95% upper confidence interval
(UCI) loading rates for hands, forearms, lower legs, and feet combined reported
in these papers are 0.35 and 0.87 mg/cm 2 , respectively, for adults and 4.8 and
7.0 mg/cm 2 , respectively, for children. The soils at both of these sites were very
sandy, resulting in approximate monolayer loadings (which is defined as the com-
plete coverage of the skin with one layer of particles) of 13 and 31 mg/cm 2 for the
adult and child scenarios, respectively.
11.7.4.3 Skin Surface Area
Dermal exposure to contaminants is affected by the surface area of skin being in
contact with the impacted media. US EPA ( 2004b ) provided recommendations for
skin surface area that may have contact with exposure media for residents and work-
ers. Updated recommendations and more detailed documentation are provided in
the Child-Specific Exposure Factors Handbook (US EPA 2008 ) and the Exposure
Factors Handbook 2009 Update (US EPA 2009 ). The recommended body surface
area estimates are based on 50th percentile values for specific body parts for the U.S.
population from the national health and nutrition examination survey (NHANES II,
see Centers for Disease Control and Prevention 2006 ) and are intended to correlate