Target and Nontarget Analyses Reveal Similar Dissolved Organic Contaminant Patterns Relative to Quantified Catchment Characteristics along Two German Rivers

River water quality is compromised by diverse organic
contaminants
from human activities. However, it is not well characterized how the
mixture of dissolved organic contaminants in rivers evolves longitudinally
from source to mouth or how it is related to river catchment characteristics.
We collected dry-weather water samples along two large, anthropogenically
impacted German rivers, the Neckar and Spree, and used target and
nontarget analyses to assess the concentration patterns of individual
organic contaminants as well as the peak area patterns of nontarget
anthropogenic features and the remaining nontarget “other”
features. 81% of the target contaminants, 66% of the anthropogenic
features, and 56% of the “other” features were detected
in at least 50% of sites in both river catchments, indicating a high
degree of chemical similarity despite catchment spatial separation.
Contaminant concentrations and feature peak areas increased within
and downstream of urbanized regions. Pharmaceuticals correlated most
strongly with the annual volume of treated wastewater effluent in
a catchment, whereas polymer-related chemicals correlated most strongly
with urban land covers linked to industry and transportation. Feature-based
molecular networks of sartans, hexa(methoxymethyl)melamine derivatives,
and polyethylene glycols revealed a multitude of contaminants in the
rivers that would be overlooked if relying on target or nontarget
annotation methods alone. This study highlights the importance of
better understanding the occurrence of chemicals related to rivers’
catchment characteristics to inform water quality management and pollution
source control.