H-t1/2 hydrolysis half-life IDLH immediately dangerous to life or health IP ionization potential K kelvin (° C + 273.15) Ka acid dissociation constant KA distribution coefficient (cm) Kb base dissociation constant Kd distribution coefficient (cm3/g) kg kilogram KH Henry’s law constant (atm · m3/mol · K) KH ¢ Henry’s law constant (dimensionless) Koc soil/sediment partition coefficient (organic carbon basis) Kom soil/sediment partition coefficient (organic matter basis) Kow n-octanol/water partition coefficient kHz kilohertz kPa kilopascal Kw dissociation constant for water (10-14 at 25 ° C) < less than £ less than or equal to L liter lb pound LC50 lethal concentration necessary to kill 50% of the aquatic species tested LC100 lethal concentration necessary to kill 100% of the aquatic species tested LD50 lethal dose necessary to kill 50% of the mammals tested lel lower explosive limit m meter m-meta (as in m-dichlorobenzene) M molarity (moles/liter) M mass meq milliequivalents mg milligram min minute(s) mL milliliter ML mass of sorbed solute mmHg millimeters of mercury mmol millimole mol mole mp melting point MS mass of solute in solution mV millivolt N normality (equivalents/liter) n-, N-normal (as in n-propyl, N-nitroso) ne effective porosity ng nanogram NIOSH National Institute for Occupational Safety and Health nm nanometer o-ortho (as in o-dichlorobenzene) OSHA Occupational Safety and Health Administration r specific density (unitless)

p-para (as in p-dichlorobenzene) P pressure Pa pascal pair vapor density of air PEL permissible exposure limit pH -log10 hydrogen ion activity (concentration) pKa -log10 dissociation constant of an acid pKb -log10 dissociation constant of a base pKw -log10 dissociation constant of water ppb parts per billion (m g/L) ppm parts per million (mg/L) P-t1/2 photolysis half-life pv specific vapor density QSAR quantitative structure-activity relationships R ideal gas constant (8.20575 ·10-5 atm · m3/mol) Ra retardation factor for an acid Rb retardation factor for a base RCRA Resource Conservation and Recovery Act Rd retardation factor Rf retention factor RTECS Registry of Toxic Effects of Chemical Substances S solubility Sa solute concentration in air (mol/L) SARA Superfund Amendments and Reauthorization Act sec-secondary (as in sec-butyl) So solubility in organics Sw solubility in water sp. species spp. species (plural) STEL short-term exposure limit sym symmetric t-tertiary (as in t-butyl; but tert-butyl) t1/2 half-life TLC thin layer chromatography TLV threshold limit value TOC total organic carbon (mg/L) Ts temperature of a substance Tw temperature of water TWA time-weighted average m micro (10-6) m g microgram uel upper explosive limit unsym unsymmetric U.S. EPA U.S. Environmental Protection Agency UV ultraviolet V, vol volume vap d vapor density Vc average linear velocity of contaminant (e.g., ft/day) vp vapor pressure

Vw average linear velocity of groundwater (e.g., ft/day) W watt l wavelength wt weight z+ positively charged species (milliequivalents/cm3)