Persistent organic pollutants associated to water fluxes and sedimentary processes in the Colorado River delta, Baja California, México

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were studied in sediment cores from two distinctive modern channels of the Colorado River (CR) delta. Their abundance and temporal changes are associated with flood-flows from the CR across the USA–Mexico border. The CR channel is directly exposed to river flood-flows while the Hardy River (HR) is a local channel derived mainly from agricultural runoff, geothermal effluents, and treated urban wastewater. Different headwater compositions and degrees of exposure to flood-flows appear to be the factors controlling the composition of persistent organic pollutants (POPs). Enrichment of OCPs (46 ng g−1 dwt in HR and 4.37 ng g−1 dwt in CR) occurred during or a few years after flooding. PCB-138 (4.2 ng g−1 dwt) is enriched in HR suggesting its origin in dielectric oils from the geothermal power plant. PCB-28 (2.1 ng g−1 dwt) in CR may be related with atmospheric input and/or re-deposition of upstream sediments. In surficial sediments (0–3 cm), only HR exceeds international sediment quality guidelines (4,4′-DDE = 8.16 ng g−1 dwt and ΣDDT = 8.34 ng g−1 dwt).

► Headwater composition and flood-flows controlling factors for organic pollutant composition.
► PCB-138 abundant probably related to dielectric oils from geothermal power plant.
► PCB-28 abundant suggest atmospheric input and/or re-deposition.
► PCB concentrations not exceed sediment quality guideline values.
► ΣDDTs and DDE exceed sediment quality guideline values.