The exposure of public to toxic substances in the air is subject to permane
nt changes which reflects the quantitative and qualitative development of t
he industrial and commercial structure as well as the increasing influence
of nonstationary (traffic caused) emission sources. At the same time the la
test scientific data lead to a change in toxicological judgement, The prese
nted paper gives an account of the general principles of assessment in envi
ronmental toxicology and corresponding legal topics, Exemplified by the dif
ficulties in determinating the exposure of the general population to partic
ulate matter these problems ave discussed.