Abstract
In order to assess the persistence of organic compounds with
global pollution potential on the basis of a minimal set of compound-specific
parameters, one of the authors has proposed a simple general law
giving a lower bound t(infinity) for the overall lifetime t of a chemical (U. Müller-Herold:
Environ. Sci. Technol. 1996, 30, 586-591).
t (infinity)
is the limiting value of t in case of in-finitely rapid exchange between
the compart-ments of the environment. This paper investigates
the accuracy of t (infinity) as an estimate for the overall
lifetime t if degradation is
much slower than transport. First, a criterion is given for degra-dation
to be slower than transport. Then t and
t (infinity)
are calculated from a 3-box unit-world model for a group of 29
relevant chemi-cals. It turns out that, for the chemicals considered,
(i) t (infinity)
is indeed a perfect estimate if degra-dation is slower than transport,
i.e., under the conditions the method has been designed for; (ii)
t (infinity)
should not be used as an approximation if the pollutant is short-lived
and its geographical range is only local; (iii) in all other cases
t (infinity)
has at least the same order of magnitude as t
.