dir.inhal.vap: dir.inhal.vap

In HumanExposure/SHEDSDevel: The SHEDS-HT model for estimating human exposure to chemicals.

Description

Models the inhalation exposure from the vapors of volatile chemicals for each theoretical person.

Usage

dir.inhal.vap(sd, cd, cprops, cb, io)

Arguments

sd	The chemical-scenario data specific to relevant combinations of chemical and scenario. Generated internally.
cd	The list of scenario-specific information for the chemicals being evaluated. Generated internally.
cprops	The chemical properties required for SHEDS-HT. The default file (the Chem_props file read in by the read.chem.props function and modified before input into the current function) was prepared from publicly available databases using a custom program (not part of SHEDS-HT). The default file contains 7 numerical inputs per chemical, and the required properties are molecular weight (MW), vapor pressure (VP.Pa), solubility (water.sol.mg.l), octanol-water partition coefficient (log.Kow), air decay rate (half.air.hr), decay rate on surfaces (half.sediment.hr), and permeability coefficient (Kp).
cb	A copy of the base data set output from the make.cbase function, with columns added for exposure variables.
io	A binary variable indicating whether the volume of the aerosol is used to approximate the affected volume.

Details

This scenario considers inhalation exposure from vapors (not aerosols). For example, painting will result in the inhalation of vapor, but it does not involve aerosols (unless it is spray paint). For this scenario, the vapor pressure and the molecular weight are relevant variables for determining exposure. These variables are included in the input to the cprops argument, which is drawn internally from the Chem_props file. The function produces a prevalence value, which reflects the fraction of the population who use this scenario at all. It also produces a frequency value, which is the mean number of times per year this scenario occurs among that fraction of the population specified by prevalence. Since SHEDS operates on the basis of one random day, the frequency is divided by 365 and then passed to the p.round (probabilistic rounding) function, which rounds either up or down to the nearest integer. Very common events may happen more than once in a day. The function also produces a mass variable, which refers to the mass of the product in grams in a typical usage event. The composition is the percentage of that mass that is the chemical in question. The evap variable is an effective evaporated mass, calculated using the mass, composition (converted from percent to a fraction), the vapor pressure as a surrogate for partial pressure, and duration of product use. The duration term is made unitless by dividing by 5 (minutes), which is an assumed time constant. The effective air concentation airconc is calculated as evap/volume. The value for airconce is capped by maxconc, which represents the point at which evaporation ceases. For chemicals used for a short duration, or with low vapor presssure, maxconc might not be reached before usage stops. Once airconc is established, the function also calculates the inhaled dose, in units of micrograms per day. The dose equals the product of exposure (g/m3), basal ventilation rate, bvr (m3/day), the METS factor of 1.75 (typically people inhale air at an average of 1.75 times the basal rate to support common daily activities), and a conversion factor of 1E6 from grams to micrograms.

Author(s)

Kristin Isaacs, Graham Glen

See Also

run, p.round, read.chem.props, Chem_props

HumanExposure/SHEDSDevel documentation built on Oct. 30, 2019, 6:49 p.m.