INTERACTIONS OF VOLATILE ORGANIC COMPOUNDS AND PARTICULATES – SPECIATION OF COPOLLUTANTS IN INDOOR AND OUTDOOR AIR ENVIRONMENTS FOR RISK ASSESSMENT

Risks associated with health effects posed by mixtures of potentially toxic organic and inorganic species in indoor and outdoor air are not easy to assess. Air is a potpourri of gases, vapors, liquid droplets, and solid particles, which are “constantly changing” in time, relative proportions, and physical distributions. Constituents are diverse chemical species and physical forms, having differing inanimate or biological origins, and manifesting disparate adverse/beneficial effects.Partitions and reactions among gaseous, liquid, and solid phases add further complications. Distinctions between biogenic particulates and inorganic particulates with sorbed organics are blurred. Consequently, risk assessments are based largely on simplifying assumptions. Total amounts of a toxic substance in all phases are considered rather than estimating the relative bioavailability in each phase. Hazard is assumed solely on effect and exposure is ignored.Speciation of particulates simply according to size is of considerable current interest. There is speculation that certain size fractions of fine particulates taken collectively, but irrespective of the presence of volatile organic and inorganic compounds (VOCs and VICs), may cause adverse health effects. In addition, gas-particle interactions of multiple chemicals make it difficult to evaluate the role of particulates in causing adverse health effects and assessing risk.Speciation of organic compounds simply according to volatility is also arbitrary. An organic compound that is volatile (VOC) in the absence of particulates may become sorbed onto a particulate surface and becomes only semivolatile (SVOC) or even nonvolatile (NVOC). Profiling of particulates with sorbed components has included: chemical abundance of elements, ions, carbon, specific organic compounds or functional groupings, isotopes, and microscopic characteristics. The National Research Council (U.S.) has identified the confounding effects of particulates interacting with VOCs as “copollutants” as a topic for future research. The intent of this paper is to “take a deep breath” and “rediscover” a few scientific perspectives: (1) what constitutes the parcel called “air”, (ii) how might its parts be speciated; (iii) how should the risks of the parts be assessed, and (iv) which parts should be best managed when and where.