Optical properties of WM are illustrated in Table . The absorption were measured as 68 the LED source will receive a lower dose than that close to the free surface. This is especially true for a liquid of low transmittance (WM), which results in a strong intensity gradient in the fluid. The volume average incident radiation was 2.18 (AFB1) and 2.24 (AFM1) mW/cm 2 . The delivered UV dose (fluence) in a stirred near collimated beam apparatus was calculated as the product of the volume average of the fluence rate in the sample and the exposure time by assuming perfect mixing of the sample by the stir bar.