The Soil Category S-1 standards are based on a residential exposure scenario in which the potential receptor may come into contact with the contaminated soil in their yard while playing or gardening. The evaluation also includes the ingestion of home-grown fruits and vegetables from a small garden.

General Methodology

The sequential approach taken to develop the MCP S-1 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) and ingestion of homegrown produce.

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-1, 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-1 Assumptions cell: K18

And,
S1 Equation 3

(equation 3)

Workbook: MCP Soil.xls Sheet: S-1 Assumptions cell: L43

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)

Ingestion of Homegrown Produce

For a limited number of chemicals (currently nine total) MADEP believes that there is sufficient information about the uptake of chemicals from soil into plants to warrant quantification of this exposure pathway. The noncancer risk-based concentration associated with ingestion of homegrown produce cultivated in contaminated soil is calculated using the following equation:
S1 Equation 4

(equation 4)

Workbook: MCP Soil.xls, Sheet: S-1, column C

parameter    description

[OHM]nc-prod = Target noncancer risk-based concentration in soil, based on ingestion of homegrown produce, (mg/kg)

HI = Target Hazard Index level (unitless)

RfDoral = chronic oral Reference Dose or equivalent toxicity value, (mg/kg/day)

Ksp = Plant Uptake Factor, (mgOHM/kgplant)/(mgOHM/kgsoil)

RAFnc-prod = Relative Absorption Factor for noncancer, oral intake of produce (unitless)

ADPIR = Average Daily Produce Intake Rate, (1/day)

The exposure term, ADPIR, is a compilation of exposure assumptions that are not chemical-specific. The factor is calculated:
S1 Equation 5

(equation 5)

Workbook: MCP Soil.xls, Sheet: Produce, cell J39

 parameter    description

ADPIR = Average Daily Produce Intake Rate, (1/day)

PIR = Daily Intake Rate of homegrown produce, (g/day)

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, (1000 g/kg)

The daily intake of homegrown produce (expressed as a dry weight) is estimated as 25% of the total daily intake of produce for a family in the Northeast of the United States, based on survey of food intake. For the evaluation of noncancer risks, data from three age groups (1-2 years, 3-5 years, and 6-7 years) are combined to result in a time weighted average daily intake, as follows:
S1 Equation 6

(equation 6)

Workbook: MCP Soil.xls, Sheet: Produce, cells B26 - D26

parameter    description

PIR1-8 = Daily Intake Rate of homegrown produce, ages 1-8 years, on a dry weight basis (g/day)

%HG = Percent of total produce consumed that is assumed to be homegrown, (unitless)

EPx = Exposure Period for each age group (x) quantified, (years)

%M = Average Percent Moisture of Produce (unitless)

IRwwx,y = Intake Rate (on a wet weight basis) of each type of produce (y), for each age group (x) quantified (grams/day)

%Cx,y = Percent of population in each age group (x) consuming each type of produce (y), (unitless)

ED = Exposure Duration, (years) 

Cumulative Noncancer Risk-Based Soil Concentration

Having calculated the target soil concentrations for direct contact (ingestion, dermal contact) and ingestion of homegrown produce separately, a target soil concentration protective of both exposure pathways is calculated using a harmonic mean:
S1 Equation 7

(equation 7)

Workbook: MCP Soil.xls, sheet: S-1, column D

parameter    description

[OHM]soil-nc = Target noncancer risk-based concentration in soil (mg/kg)

[OHM]nc-dc = Target noncancer concentration in soil based on direct contact (mg/kg)

[OHM]nc-prod = Target noncancer concentration in soil based on ingestion of homegrown produce (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) and ingestion of homegrown produce.

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-1, column: E

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-1 Assumptions cell: K26

And,
S1 Equation 10

(equation 10)

Workbook: MCP Soil.xls Sheet: S-1 Assumptions cell: L51

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)

Ingestion of Homegrown Produce

For a limited number of chemicals (currently nine total) MADEP believes that there is sufficient information about the uptake of chemicals from soil into plants to warrant quantification of this exposure pathway. The cancer risk-based concentration associated with ingestion of homegrown produce cultivated in contaminated soil is calculated using the following equation:
S1 Equation 11

(equation 11)

Workbook: MCP Soil.xls, Sheet: S-1, column F

parameter    description

[OHM]ca-prod = Target cancer risk-based concentration in soil, based on ingestion of homegrown produce, (mg/kg)

ELCR = Target Excess Lifetime Cancer Risk level (unitless)

Ksp = Plant Uptake Factor, (mgOHM/kgplant)/(mgOHM/kgsoil)

RAFca-prod = Relative Absorption Factor for cancer, oral intake of produce (unitless)

CSForal = Oral Cancer Slope Factor, (mg/kg/day)-1

LADPIR = Lifetime Average Daily Produce Intake Rate, (1/day)

The exposure term, ADPIR, is a compilation 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 factor is a time-weighted average, as calculated by the following equation:
S1 Equation 12

(equation 12)

Workbook: MCP Soil.xls, Sheet: Produce, cell J47

parameter    description

LADPIR = Lifetime Average Daily Produce Intake Rate, (1/day)

PIRx = Daily Intake Rate of homegrown produce specific to each age group, (g/day)

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, (1000 g/kg)

The daily intake of homegrown produce (expressed as a dry weight) is estimated using equation 3-6 for the appropriate age groups (1-31 years).

Cumulative Cancer Risk-Based Soil Concentration

Having calculated the target soil concentrations for direct contact (ingestion, dermal contact) and ingestion of homegrown produce separately, a target soil concentration protective of both exposure pathways is calculated using a harmonic mean:
S1 Equation 13

(equation 13)

Workbook: MCP Soil.xls, sheet: S-1, column G

parameter        description

[OHM]soil-ca = Target cancer risk-based concentration in soil (mg/kg)

[OHM]ca-dc = Target cancer concentration in soil based on direct contact (mg/kg)

[OHM]ca-prod = Target cancer concentration in soil based on ingestion of homegrown produce (mg/kg)

Input Parameters

The Method 1 S-1 Soil Standards are based on an assumed residential exposure to soil by children and adults during play and gardening

FactorAgeValueUnitsComment
Body Weight (BW)    
 1-816.8kgThis value is the arithmetic average of the median (50th %-tile) body weights for each year in this age group (females).
 8-1539.7kg
 15-3054.2kg
Soil Ingestion Rate (IRsoil)
 1-8100mg/dayMADEP (1995), Appendix B
 8-3050mg/day
Skin Surface Area (SSA)
 1-82,431cm2Average of Median values of the Face, Hands, Forearms, Lower Legs and Feet for each age group. (EPA, 1997)
 8-154,427cm2
 15-305,653cm2
Soil Adherence Factor (SAF)

1-8

8-15

15-30

0.35

0.14

0.13

mg/cm 2Weighted average of adherence factors for specific body parts exposed (MA DEP 2002)
Produce Intake Rate, wet weight (IRww)
 1-301 - 76grams/dayMean values, age- and vegetable-specific. (USDA)
Percent Homegrown (%HG)
 1-3025%Assumes 100% of consumed produce is homegrown during 3-month growing season, 0% remaining 9 months.
Percent of Individuals Consuming a Vegetable (%C)
 1-302 - 50.9%Age- and vegetable-specific for northeast U.S. (USDA)
Exposure Frequency (EF)
Direct Contact
    
EF1
1-305days/week 
EF2
1-3030weeks/year 
Produce Intake
    
EF1
1-307days/weekSince produce intake rates are calculated as an annual daily average, EF must reflect a daily exposure.

EF2

1-3052weeks/year
Exposure Period (EP)
Noncancer
1-87years30 years is approximately the 90 th percentile value for residence time. (USEPA, 1997)

Cancer

1-3030years
Averaging Period (AP)
Noncancer
1-87yearsEqual to EP for noncancer risk, a lifetime for cancer risk.

Cancer

1-3070years