Variability of Biodegradation Rates of Commercial Chemicals in Rivers in Different Regions of Europe

Biodegradation is one of the most important processes
influencing
the fate of organic contaminants in the environment. Quantitative
understanding of the spatial variability in environmental biodegradation
is still largely uncharted territory. Here, we conducted modified
OECD 309 tests to determine first-order biodegradation rate constants
for 97 compounds in 18 freshwater river segments in five European
countries: Sweden, Germany, Switzerland, Spain, and Greece. All but
two of the compounds showed significant spatial variability in rate
constants across European rivers (ANOVA, P < 0.05).
The median standard deviation of the biodegradation rate constant
between rivers was a factor of 3. The spatial variability was similar
between pristine and contaminated river segments. The longitude, total
organic carbon, and clay content of sediment were the three most significant
explanatory variables for the spatial variability (redundancy analysis, P < 0.05). Similarities in the spatial pattern of biodegradation
rates were observed for some groups of compounds sharing a given functional
group. The pronounced spatial variability presents challenges for
the use of biodegradation simulation tests to assess chemical persistence.
To reflect the variability in the biodegradation rate, the modified
OECD 309 test would have to be repeated with water and sediment from
multiple sites.