Human and Ecological Risk Office

LeadSpread-9

A tool for evaluating exposure and the potential for adverse health effects resulting from exposure to lead in the environment.

LeadSpread was created to run on Microsoft Excel.

Background:  Historically, LeadSpread has been a tool used by DTSC to estimate blood lead concentrations resulting from exposure to lead in soil at contaminated properties.  Exposure via the ingestion, inhalation, and dermal pathways is represented by equations relating incremental blood lead increase to the soil lead concentration to provide an estimate of median blood lead concentration.  Upper percentile blood lead concentrations, ninetieth (90^th) up to ninety-fifth (95^th) are estimated from the median value by assuming a log-normal distribution with a geometric standard deviation (GSD) of 1.6.

The toxicity criterion on which LeadSpread 9 is based is CalEPA’s Office of Environmental Health Hazard Assessment’s (OEHHA) toxicity evaluation of lead with a source-specific “benchmark change” of 1 µg/dL which is the estimated incremental increase in children’s blood lead that would reduce IQ by up to 1 point.  Because two key exposure parameters utilized in LeadSpread have been updated since the previous version of LeadSpread (LeadSpread 8), LeadSpread 9 was developed.

LeadSpread 9 is a revision of LeadSpread 8 and should be used for evaluating residential and industrial land use scenarios.  Three exposure scenarios are provided in LeadSpread 9.  The first is a child exposure scenario which evaluates exposure to a residential child.  The other two are an adult residential scenario and an adult industrial scenario.  The latter incorporates DTSC recommendations for evaluating industrial worker exposures to lead in soil.  Both adult scenarios are based on the need to protect the fetus carried by an exposed adult female such that the incremental increase in blood lead of the fetus does not exceed 1 µg/dL.

In addition to showing estimated blood lead levels resulting from the lead concentration at the site, LeadSpread displays the Preliminary Remedial Goal (PRG) for the site.  The PRG is a soil lead concentration leading to an incremental increase in blood lead of 1 µg/dL.  The PRG is based on the OEHHA benchmark dose and is meant to be implemented as an estimate of the Exposure Point Concentration (EPC) of lead at the site after remediation.  The EPC is usually based on the 95th percentile upper confidence limit on the arithmetic mean, as a “not to exceed” soil concentration.  Because the lead benchmark dose is an incremental change in blood lead, background exposures to lead, and media other than soil, or dust from the site which may be impacted by lead are not considered in the worksheet.  If lead is present in media other than soil (e.g., water, air) or if the home grown produce pathway is anticipated at the site, please contact the HERO toxicologist assigned to the site.

Using the previous, version of LeadSpread, LeadSpread 8, a Preliminary Remedial Goal of 77 mg/kg soil lead was estimated.  A value of 70 mg/kg soil lead is estimated using LeadSpread 9.  For most sites without special circumstances, such as markedly elevated soil lead bioavailability, the difference in predicted incremental blood lead and IQ change for exposures to soil lead between 70 mg/kg and 77 mg/kg is within the LeadSpread model uncertainty and does not exceed the de minimis level of 1 IQ point identified by OEHHA.  The current DTSC residential lead (Pb) soil screening level is 80 mg/kg, based on an estimated increase in blood Pb in a 90^th percentile child of 1 µg/dL.  At 80 mg/kg soil lead, LeadSpread 9, estimates the increase in blood Pb in a 90^th percentile child as 1.14 µg/dL which, in turn, is associated with an upper-bound estimate of a loss of 1 IQ point.  The change is not discernable at one significant figure.  Results of IQ tests are reported as an integer.  Fractional IQ points are not measured.  The blood lead level of 1.14 would have to rise  to 1.5 (which would round up to 2.0) to be considered a significant increase.  Therefore, HERO recommends that the remedial/mitigation level for residential soil exposure remain at the current residential default value of 80 mg/kg.  Future development of better-defined childhood exposure parameters may change this recommendation.

Download “LeadSpread-9-March-2022A.xlsx” workbook

Documentation for the Worksheet is contained as comments for various cells within the worksheet.  For convenience, major comments and notes are contained in the separate link below.

Download “LeadSpread 9- INFORMATION FOR USERS”

Frequently Asked Questions (FAQ) related to LeadSpread-9 are contained in the link below.   

Download LeadSpread-9 Frequently Asked Questions

NOTE: If you have questions regarding LeadSpread 9 or evaluation of lead exposures, please include them in an e-mail message to LeadSpread9.Questions