care is also required in interpretimg concentrationdata, since the processes descried are not always similar,the animal type and size varies wideiy and concentrations are inevitably influenced by water consumption. the best basic for expressing and comparing pollution output and water use is the use of an equivaient dressed carcass weight, since comparison of data between mixed species facilities and animals of different carcass weights is then possibie.unfortumately, data are rarely published in this form and the latest publiahed figures remain those of witherow, 1973 (table 3).