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

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.

2008年至2019年旱季过后的雨季期间，研究人员采集美国加利福尼亚州圣克鲁兹市圣洛伦索河的河水样本，以分析其中的多环芳烃（polycyclic aromatic hydrocarbons，PAHs）与悬浮泥沙浓度（suspended sediment concentrations，SSC）。采样工作借助部署于人行天桥下方桥箱式平台的美国D-95型积深式采水器完成。针对每份悬浮泥沙样本，采集的水样被装入连接至采样装置的1升耐洁（Nalgene）瓶中。静置14天后，通过真空泵的湿式抽吸法去除瓶内多余水分与有机质，随后利用0.063毫米孔径的筛网过滤，将砂粒组分与粉砂、黏土组分分离。将砂粒、粉砂-黏土两类组分分别置于坩埚中，于103摄氏度的烘箱内烘干后称重。针对多环芳烃分析，采样装置配备经酸清洗、甲醇润洗的特氟龙（Teflon）瓶与喷嘴，用于开展积深采样。每次采样采集四份1升装特氟龙瓶水样，随后将水样小心转移至4.0升的棕色玻璃瓶中，并加入30毫升Optima级二氯甲烷。样品采用液液萃取法提取后进行浓缩，再注入气相色谱-质谱联用仪（gas chromatograph/mass spectrometer，GC/MS）进行分析。多环芳烃浓度通过内标法计算，回收率则采用氘代多环芳烃替代标准品测定。所有多环芳烃样品均经过空白校正，阳性鉴定结果基于参考标准品及/或已知谱图得出。