Organic contaminants in peninsula berms and agricultural soils at the Sonoma Baylands Wetland Demonstration Project site and adjacent seasonal wetlands, Sonoma County, California

Abstract

A geochemical study was conducted to establish baseline data of organic contaminants in soils of artificial peninsulas developed as barriers, at the Sonoma Baylands Wetland Demonstration site. This study also included soils of the adjacent hayfields, Leonard Ranch, and North Point Properties, which are seasonal wetlands. This information is helpful as reference data for monitoring the progress of wetland development and restoration. Compounds were identified by gas chromatography/mass spectrometry, and included aliphatic hydrocarbons, biomarker hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), chlorinated pesticides DDT and its degradates DDD and DDE, chlordanes, and dieldrin. Aliphatic and biomarker hydrocarbons are mainly biogenic, whereas the PAHs and chlorinated pesticides are mainly anthropogenic. Ratios of DDE/DDT were less than 1.0, indicating that the DDT in these soils has not been subjected to significant long term weathering. Concentrations of total DDTs were the greatest in soils from the North Point Properties (9.7 ng/g, or ppb). Concentrations of total PAHs were the greatest in soils from Leonard Ranch (680 ng/g) and peninsula 15 at the Main site (600 ng/g). Concentrations of total PAHs and DDTs in soils were generally below the Effects Range-Low values. Therefore, the potential for toxic effects to biota that may be exposed to these soils is low, making these soils suitable for wetland construction and restoration.