The Soil Category S-2 standards are based on an adult exposure scenario in which the potential receptor may come into frequent but passive contact with the contaminated soil.

General Methodology

The sequential approach taken to develop the MCP S-2 Soil standards is as follows:

Step

Description

 

1.

A noncancer risk-based concentration associated with 20% of an allowable daily intake is identified.

2.

A cancer risk-based concentration associated with an excess lifetime cancer risk of one-in-one million (10-6) is identified.

3.

A leaching-based concentration (a level in soil considered protective of the applicable groundwater standard) is identified. (Workbook: MCP Leach.xls, Sheet: Leaching, columns: H-J)

4.

A ceiling concentration is identified. The ceiling concentration varies by category, as described below. (Workbook: MCP Toxicity.xls, sheet: Toxicity, columns BJ - BQ)

5.

The lowest of the concentrations identified in steps 1 through 4 is carried through the process.

6.

A Practical Quantitation Limit (PQL) for an appropriately sensitive analytical method is identified (Workbook: MCP Toxicity.xls, sheet: Toxicity, column: AP).

7.

A background concentration is identified, if available (Workbook: MCP Toxicity.xls, sheet: Toxicity, column: AD).

8.

The highest of the three values identified in steps 5, 6 and 7 is chosen.

9.

The value identified in step 8 is rounded to one significant figure. This value is adopted as the Method 1 Soil Standard for the specified soil category.

 

This process is diagramed:

Diagram of S-1 Development Methodology
 

Equations

Noncancer Risk-Based Soil Concentrations

The noncancer risk-based concentration of a chemical in soil is a function of the direct contact exposure (ingestion, dermal contact).

Direct Contact: Ingestion & Dermal Exposures

The noncancer risk-based concentration associated with direct contact with contaminated soil is calculated using the following equation:

S1 Equation 1 (equation 1)

Workbook: MCP Soil.xls, Sheet: S-2, column: B

parameter
 
description

[OHM]nc-dc
=
Target noncancer risk-based concentration in soil, based on direct contact (ingestion and dermal exposure) with the soil, (mg/kg)
HI
=
Target Hazard Index level (unitless)
RfDoral
=
chronic oral Reference Dose or equivalent toxicity value, (mg/kg/day)
ADSIR
=
Average Daily Soil Ingestion Rate, (1/day)
RAFnc-ing
=
Relative Absorption Factor for noncancer, oral exposures (unitless)
ADSDCR
=
Average Daily Soil Dermal Contact Rate, (1/day)
RAFnc-dermal
=
Relative Absorption Factor for noncancer, dermal exposures (unitless)

The exposure terms, ADSIR and ADSDCR, are compilations of exposure assumptions that are not chemical-specific. They are calculated as follows.

S1 Equation 2 (equation 2)

Workbook: MCP Soil.xls Sheet: S-2 Assumptions cell: J21

And,

S1 Equation 3 (equation 3)

Workbook: MCP Soil.xls Sheet: S-2 Assumptions cell: K43

parameter
 
description

ADSIR
=
Average Daily Soil Ingestion Rate, (1/day)
IRsoil
=
Soil Ingestion Rate, (mg/day)
ADSDCR
=
Average Daily Soil Dermal Contact Rate, (1/day)
SSA
=
Average Daily Skin Surface Area Exposed, (cm2/day)
SAF
=
Soil Adherence Factor, (mg/cm2)
EF1
=
Exposure Frequency (days/week)
EF2
=
Exposure Frequency, (weeks/year)
EP
=
Exposure Period, (years)
BW=Body Weight (kg)
AP=Averaging Period (years)
C1=Conversion Factor (365 days/year)
C2
=
Conversion Factor (106 mg/kg)

Cancer Risk-Based Soil Concentrations

The cancer risk-based concentration of a chemical in soil is a function of the direct contact exposure (ingestion, dermal contact).

Direct Contact: Ingestion & Dermal Exposures

The cancer risk-based concentration associated with direct contact with contaminated soil is calculated using the following equation:

S1 Equation 8 (equation 8)

Workbook: MCP Soil.xls, Sheet: S-2, column: C

parameter
 
description

[OHM]ca-dc
=
Target cancer risk-based concentration in soil, based on direct contact (ingestion and dermal exposure) with the soil, (mg/kg)
ELCR
=
Target Excess Lifetime Cancer Risk level (unitless)
LADSIR
=
Lifetime Average Daily Soil Ingestion Rate, (1/day)
RAFca-ing
=
Relative Absorption Factor for cancer, oral exposures (unitless)
LADSDCR
=
Lifetime Average Daily Soil Dermal Contact Rate, (1/day)
RAFca-dermal
=
Relative Absorption Factor for cancer, dermal exposures (unitless)
CSForal
=
Oral Cancer Slope Factor, (mg/kg/day)-1

The exposure terms, LADSIR and LADSDCR, are compilations of exposure assumptions that are not chemical-specific. Since the cancer risk calculations include exposures that occur over three age groups (1-8 years, 8-15 years, and 15-31 years), the factors are time-weighted averages, as calculated by the following equations:

S1 Equation 9 (equation 9)

Workbook: MCP Soil.xls Sheet: S-2 Assumptions cell: J29

And,

S1 Equation 10 (equation 10)

Workbook: MCP Soil.xls Sheet: S-2 Assumptions cell: K51

parameter
 
description

LADSIR
=
Lifetime Average Daily Soil Ingestion Rate, (1/day)
IRsoil,x
=
Soil Ingestion Rate, specific to each age group, (mg/day)
LADSDCR
=
Lifetime Average Daily Soil Dermal Contact Rate, (1/day)
SSAx
=
Average Daily Skin Surface Area Exposed, specific to each age group (cm2/day)
SAFx
=
Soil Adherence Factor, specific to each age group (mg/cm2)
EF1,x
=
Exposure Frequency specific to each age group (days/week)
EF2,x
=
Exposure Frequency specific to each age group (weeks/year)
EPx
=
Exposure Period specific to each age group (years)
BWx
=
Body Weight specific to each age group (kg)
AP=Averaging Period (years)
C1=Conversion Factor (365 days/year)
C2=Conversion Factor (106 mg/kg)

Input Parameters

The Method 1 S-2 Soil Standards are based on an assumed passive adult exposure to soil.

Factor

Age

Value

Units

Comment


Body Weight (BW)

 

18-45

61.1

kg

This value is the arithmetic average of the median (50th %-tile) body weights for each year in this age group (females).
Soil Ingestion Rate (IRsoil)
 18-4550mg/day

MADEP (1995), Appendix B

Skin Surface Area (SSA)
 18-453,473cm2

Average of median values of the face, hands, forearms, lower legs and feet for adult females. (EPA, 1997)

Soil Adherence Factor (SAF)

 

18-45

0.03

mg/cm2

Weighted average of adherence factors for specific body parts exposed (MA DEP 2002)

Exposure Frequency (EF)
EF1
18-454days/weekEF reflects frequent exposure during warmer months.
EF2
18-4530weeks/year
Exposure Period (EP)
 
18-4527years

Upper percentile value, consistent with long-term employment.

Averaging Period (AP)
Noncancer
18-4527years

Equal to EP for noncancer risk, a lifetime for cancer risk.

Cancer

18-45

70

years