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Polycyclic aromatic hydrocarbons (PAHs) and suspended sediment concentrations in the San Lorenzo River, Santa Cruz, California, USA

January 28, 2022

Water from the San Lorenzo River in Santa Cruz, California, was sampled to analyze for polycyclic aromatic hydrocarbons (PAHs) and suspended sediment concentrations (SSC) during the rainy seasons from 2008 to 2019 following drought conditions. The samples were collected using a US D-95 depth-integrated water sampler deployed from a bridge-box platform beneath a pedestrian bridge For each suspended-sediment sample, the water was collected in a 1-liter Nalgene bottle attached to the sampling device. After 14 days of settling time, excess water and organic matter were removed from the bottle using wet suction from a vacuum pump, and the sand fraction was then separated from silt and clay by filtration through a 0.063 mm sieve. Each fraction (sand and silt-plus-clay) was dried in a crucible in a 103-degree Celsius oven, and then weighed. For the PAH analyses, depth-integrated sampling was conducted using acid-cleaned, methanol-rinsed Teflon bottles and nozzles attached to the sampling device. Samples (four 1-liter samples for each deployment) from the Teflon bottles were carefully transferred to a 4.0 L amber glass bottles and spiked with 30ml of Optima -grade dichloromethane. The samples were extracted using a liquid-liquid extraction and concentrated prior to injection and analysis on a gas chromatograph/mass spectrometer (GC/MS). PAH concentrations were calculated using internal standards and recoveries were determined using deuterated PAH surrogate standards. All PAH samples were blank corrected and positive ID was based on reference standards and/or known spectra.