medium. These aspects have been discussed extensively by Gillet et a1 . 

 1974). 



Interfacial processes can be broken down into two categories: (1) 

 Interfacial interactions not involving changes of the contaminant, but which 

 result in the exchange of the compound with the dispersive medium (soil, 

 water and air), and (2) all chemical reactions, abiotic or biotic, that al- 

 ter the chemical structure of the compound. Interfacial interactions not 

 involving changes of the comtaminant include volatilization, dissolution and 

 sorption (adsorption and absorption), molecular associations such as chela- 

 tion, hydrogen bonding, ionic interactions, etc. These physico-chemical 

 interactions are important because contaminants may not only be immobilized, 

 but that can also mediate mobilization and transport as reported by Ogner 

 and Schnitzer (1970). Also, the interactions art amenable to classical 

 physico-chemical treatment and interpretations. In addition, chemical 

 structure is a crucial aspect, not only as a flow-factor, but also in toxi- 

 city (Addison and Cote 1973; Cohen et al . 1974; Kapoor et al_. 1973; 

 Kopperman et al_. 1974; Sugawara 197^ VTlceanu et al_. 1972; Wildish 1974). 



Studies on abiotic noninterfacial transformation reactions (photode- 

 gradation, hydrolysis, etc.) have been conducted for only a few organic com- 

 pounds (Crosby and Leitis 1973; Crosby and Moilanen 1973; Crosby and 

 Moilanen 1974; McGuire et al^. 1970; Pope et al^. 1970; Pope and Zabik 1970; 

 Ruzo et ^. 1972; Zabik et ^. 1971). Consequently an assessment of their 

 importance to ecosystem transport and availability is virtually impossible. 

 However, the results obtained from certain toxicological investigations in- 

 volving pesticides suggest that biotransformations may activate or deacti- 

 vate the parent compound to more or less toxic metabolities (O'Brien 1967; 

 O'Brien and Yamamoto 1970). Since the biological availability of organic 

 chemicals is of critical importance to evaluating toxicity, and thereby po- 

 tential ecosystem malfunction, the development of useful transformations 

 and interfacial exchange features has been undertaken. 



The degree of bioaccumulation as a function of the available concentra- 

 tions in the medium can be predicted. Recent studies by Neeley et al . 

 (1974) have shown that the octanol/water partition coefficients for organic 

 chemicals are linearly correlated with bioaccumulation in fish. Correlating 

 the octanol/water quantities and environmental concentrations for a series 

 of chemicals may prove useful in providing a rapid screening technique for 

 predicting environmental concentrations. In addition, computerized treat- 

 ment of residue data from aquatic organisms continuously exposed to contami- 

 nants is actively being developed. The uptake phase is usually 28-56 days 

 and the elimination phase is 28 days (Figure 1). Accelerated bioconcentra- 

 tion tests of only 4 days have been used with some chemicals to predict bio- 

 concentration under longer exposures (Branson et a]^. 1975). 



ENVIRONMENTAL HAZARD EVALUATION 



The Toxic Substances Control Act of 1976 clearly indicates that an "un- 

 reasonable risk" of injury to health or the environment caused by manufac- 

 ture, distribution, use, or disposal is needed to establish a chemical as 



52 



