ADDED RISK APPROACH TO DERIVE MAXIMUM PERMISSIBLE CONCENTRATIONS FOR HEAVY-METALS - HOW TO TAKE NATURAL BACKGROUND LEVELS INTO ACCOUNT

A unified method is presented to derive maximum permissible concentrat ions (MPCs) of xenobiotic and naturally occurring substances, The meth od relies upon risk limitation expressed as the maximum potentially af fected fraction of all possible species (PAF(max)) in a component ecos ystem, due to a bioavailable concentration of the considered substance , For xenobiotic compounds the method is simplified to the ''HC5 appro ach,'' i.e., the MPC equals the hazardous concentration at which 5 % o f the species are unprotected, If the natural background of a substanc e is (partly) bioavailable, the related background effect, also expres sed as PAF, is taken into account in deriving a MPC. Examples are give n and MPCs for zinc, chromium, cadmium, copper, and lead for different levels of bioavailability in water are developed. (C) 1997 Academic P ress.