substituted biphenyls, hydroquinone (m-dihydroxy benzene),

and catechol (o-dihydroxy benzene) (Moore and Ramamoorthy,

1984). Photolysis of phenol to hydroquinone occurs under

both natural sunlight and commercial sun lamps (USEPA,

1979).

 Assuming a first order reaction, the rate of

disappearance of an organic compound by direct photolysis

from surface water is

 -dC/dt = K [C] = k 10 (e-qz) [C] (3-7)

where C is the concentration of the compound, K is the

apparent first-order photolysis rate constant, k is a

constant of proportionality which includes the quantum yield

of the reaction, I0 is the solar radiation intensity at

photochemically active wave lengths incident on a water

surface, q is the extinction coefficient of the water (which

is a function of dissolved and particulate absorbers), and z

is the depth (Pignatello et al., 1983). Equation (3-7) can

be converted into a mathematically calculable form:

 In ( C / Co ) = k 1 (e-qz) [C] (3-8)

 One EPA report (1979) stated that 2,4-DCP and PCP do

undergo photolysis but its significance and environmental

importance is uncertain. However, Hwang et al. (1986)

indicated that in summer time K values for 2,4-DCP and PCP

were 1.0 and 0.37 h-, respectively at a depth of 3cm while
 -l
compared to 0.016 h- for phenol. A similar result for PCP

photolysis was reported by Pignatello et al. (1983). Crosby

(1981) concluded that in either water or organic solvents,