MPCA Remediation Division updates on Health Based Values

The MPCA Remediation Division has issued updates regarding the following health based values:

 

•             Blood Lead Level Rationale

•             Interim TCE ISV

•             Interim cis-1,2-DCE ISV

 

This information will also be posted within the next week on the MPCA’s Remediation Division webpage at http://www.pca.state.mn.us/qwrhkh4 (under the Guidance Section).

 

Rationale for the use of 10 ug/L Lead Blood Level

Background

On January 4, 2012, the Center for Disease Control’s (CDC) Advisory Committee for Childhood Lead Poisoning Prevention (ACCLPP) released a report regarding children blood lead levels (BLL). ACCLPP recommended eliminating the use of the term “blood lead level of concern” and replace it with the term “blood lead reference level” since they determined there was no safe level of lead exposure. They also recommended the use of a blood lead reference level of 5 µg/dL (opposed to the previously recommended 10 µg/dL) in children to trigger medical and prevention actions.

MPCA uses EPA’s child lead model to derive the residential lead soil reference value (SRV) and adult lead model to derive the industrial lead SRV. In some cases, MPCA also allows site specific lead modeling to derive a site specific lead SRV. In these cases MPCA may use professional judgment to determine a “do not exceed” level.

At this time, EPA’s Superfund program is not recommending the use of CDC’s new 5 µg/dL blood lead level in the current version of their child lead model (Integrated Exposure Uptake Biokinetic or IEUBK) or their Adult Lead Model.

On March 15, 2013, MPCA requested guidance from MDH regarding the most appropriate lead blood level to use in deriving statewide and site specific SRVs.

MDH Guidance

MDH responded to MPCA’s request on March 25, 2013 stating that they recommended the use of CDC’s lead reference level of 5 µg/dL for the purpose of modeling exposure levels and pathways and developing clean-up guidance. MDH also added that this was a policy decision since MDH is unable to calculate a safe level of exposure.

MPCA Policy Decision

EPA’s Superfund program has recently announced they are releasing a new version of the child lead model (IEUBK) sometime this year (2013) that contains revised exposure parameters in addition to CDC’s new blood lead level. Preliminary results from EPA’s revised model show that residential lead SRVs may not decrease and if they do decrease that decrease will not be as significant as it would be using the current model and the new CDC lead blood level. At this time it is not clear what EPA will advise regarding the Adult Lead Model or how it may impact the industrial SRV.      

MPCA will continue to use 10 µg/dL for site specific lead modeling and to derive lead SRVs. However, responsible parties must be aware that MPCA will be adopting the new lead blood level for the residential lead SRV once EPA releases the new version of the child lead model (IEUBK). MPCA will also be adopting any changes EPA recommends regarding the Adult Lead Model that may result in a change in the industrial SRV once those are released. Responsible parties may be required to perform additional lead clean up based on these changes.

 

Trichloroethylene (TCE) Interim ISV

Table 1. Interim TCE ISVs

ISV Land Use Category	Current ISV (µg/m3)	Basis	Revised Interim ISV (µg/m3)	Basis
Residential	3	Cancer	2	Noncancer
Industrial	8	Cancer	6	Noncancer

 

New toxicity data released by EPA’s Integrated Risk Information System (IRIS) in September of 2011 results in a decrease in both the residential and industrial trichloroethylene (TCE) ISVs. The “Revised Interim ISV” values listed in the table above should be used for Remediation Vapor Intrusion Investigations until the ISV spreadsheet can be fully revised sometime later this year.

 

Additional Information:

The current ISVs are based on cancer risks. In September, 2011, EPA’s IRIS released a new inhalation unit risk (IUR) of 4.1E-06 µg/m³ (used to assess cancer risks) and a new reference concentration (RfC) of 2 µg/m³ (used to assess noncancer risks). Since the new noncancer toxicity value (RfC) shows a greater risk than the new cancer toxicity value (IUR) the revised interim ISVs are now based on noncancer risks. To provide clarity, the residential and industrial cancer ISVs are listed in Table 2. However, the final ISVs to be used for Remediation Vapor Intrusion Investigations are based on the noncancer values listed in Table 1.

 

Table 2. TCE Cancer ISVs

ISV Land Use Category	Revised Cancer ISV (µg/m3)	Basis
Residential	2	Cancer
Industrial	20	Cancer

 

Cis-1,2-Dichloroethene (1,2-DCE) Interim ISV

Table 1. Cis-1,2-Dichloroethene ISVs

ISV Land Use Category	Revised Interim ISV (µg/m3)	Basis
Residential	60	Noncancer
Industrial	200	Noncancer

 

Based on discussions with EPA and MDH, it is appropriate to use the trans-1,2-dichloroethene inhalation toxicity value (reference concentration, RfC) as a surrogate for cis-1,2-dochloroethene. The cis-1,2-dichloroethene ISVs listed in Table 1 should be used for screening purposes.  It is important to keep in mind that this is a surrogate and not a toxicity value specific to cis-1,2-dichlorethene.  If this ISV is exceeded it does not indicate that a risk exists. An exceedance indicates that a more thorough investigation should be conducted to determine if a risk exists.