Fizzy Effect

According to the Sixth Doctor, the so-called Fizzy Effect signified that he and Peri Brown had landed somewhere between 1970 and 1974 which was when the early experiments in Colour Seperation Overlay were being conducted.

Peri gave the description of the people affected appearing "blurry as though disintegrating", initially believing the effect to have been a product of a radioactive holocaust. The Doctor and Peri observed many people, including the Third Doctor and Brigadier Lethbridge-Stewart with the effect. (NOTVALID: Doctor Who? 108)

Behind the scenes
The Fizzy Effect is a reference to the entire Third Doctor era on television which ran from 1970 to 1974 and regularly employed somewhat primitive CSO which gave the effect described in the story.