Biodegradation Rates of Organic Chemicals in a Subtropical River: From Laboratory to Field

Understanding the
attenuation rate of organic chemicals in aquatic
environments is essential for assessing their long-term ecological
risks and informing chemical management. Biodegradation is a key attenuation
pathway for many chemicals, however, measuring biodegradation in situ
is inherently complex, resource-intensive, and subject to high environmental
variability. Consequently, regulatory frameworks and research efforts
often rely on laboratory tests, intended to provide controlled and
reproducible conditions. Despite their widespread application, few
studies have evaluated how well these laboratory results represent
biodegradation in real aquatic environments. In this study, we compared
biodegradation rate constants (k) from a modified
OECD 309 laboratory test with those derived from a field experiment
in a subtropical river (Queensland, Australia). Biodegradation was
measurable in both laboratory and field experiments for 23 chemicals
spanning diverse structures. Rank-order agreement between laboratory k and field k was strong (Spearman ρ = 0.7, p < 0.001), and linear
association was high (Pearson r = 0.8, p < 0.001) for the 16 chemicals that did not sorb strongly. The
relative magnitudes of laboratory and field log k also aligned well (slope of the linear regression = 0.8), however,
uncertainty remained (average root-mean-square-error equivalent to
a factor of 2). These results demonstrate that the modified OECD 309
can capture much of the rank-order and relative magnitude of biodegradation,
supporting its role as a higher-tier laboratory simulation test for
persistence assessment.