From Freshwater to Marine Environments: Spatial Variation in Chemical Biodegradation Rates Applying a Modified OECD 309-Type Experiment

The
rate of biodegradation in aquatic environments is a large source
of uncertainty in chemical exposure assessments. Currently, there
are insufficient biodegradation data and limited understanding of
spatial variation in biodegradation, particularly across diverse aquatic
environments. This study investigated the spatial variation in chemical
biodegradation rate constants (k) across seven distinct
aquatic environments in Australia including marine, mangrove, estuarine,
and freshwater ecosystems, using a modified OECD 309 test. Significant
spatial variation in k was found for 36 of 38 chemicals
(ANOVA, p < 0.05). In addition, the average log k for the chemicals was strongly correlated with the average
log k of the same chemicals in 18 European
rivers measured using the same method (Pearson r =
0.94, p < 0.001), illustrating intercontinental
consistency in the relative biodegradation behavior of the chemicals.
However, the standard deviation in log k (which
is a relative metric equivalent to a fold difference) was larger across
the Australian sites than across the European sites for many chemicals.
These findings provide two key insights: first, that diverse aquatic
environments demonstrate greater spatial variability in k than rivers; and second, that despite this spatial variability,
the modified OECD 309 method can reliably rank chemicals according
to their biodegradability and thus be useful in persistence assessments.