Bight 23 Sediment Chemistry Harmonized

The Southern California Bight 2023 Regional Monitoring Program (Bight '23) is the seventh in a series of regional marine monitoring efforts starting in 1994 and repeating every five years thereafter. This report presents the results of the sediment chemistry portion of the survey, which is one component of the Sediment Quality element of the Bight '23 program. The sediment chemistry element addressed two primary questions: (1) What is the extent and magnitude of sediment chemistry exposure in the Southern California Bight (SCB)? and (2) How does the extent and magnitude of sediment chemistry exposure vary over time in the SCB? A stratified random sampling design was used, encompassing ten strata including three continental shelf depth strata (inner: 5-30 m, middle: 30-120 m, outer: 120-200 m), upper slope (200-500 m), lower slope (500-1000 m), Channel Islands (30-120 m), and four embayment strata (marinas, ports, bays, and estuaries). A total of 340 stations were sampled between July and October 2023. Sediment samples were analyzed for grain size, total organic carbon, total nitrogen, 15 trace metals, polycyclic aromatic hydrocarbons (PAHs, sum of 24 compounds), polychlorinated biphenyls (PCBs, sum of 43 congeners), dichlorodiphenyltrichloroethane compounds (DDTs), and chlordanes. Five groups of organic constituents of emerging concern (CECs) were also measured, including polybrominated diphenyl ether (PBDE) flame retardants, pyrethroid compounds, neonicotinoid insecticides, one tire-wear compound (6-PPD-quinone), and two per- and polyfluorinated alkyl substances (PFAS: PFOS and PFOA). An estimated 83% of the sediment seafloor Bight-wide were considered minimal to low exposure according to California's Sediment Quality Objectives (SQO) assessment framework, with only 1% in the high exposure category. Contamination was generally greater in embayments than offshore strata. Over the five surveys from 2003 to 2023, the areal extent of sediment condition meeting SQO guidelines ranged from 61% to 83%, with apparent but not statistically significant improvements over time except in the slope strata. New analytes introduced in Bight '23 included PFAS, neonicotinoid insecticides, and tire-wear compounds, which were generally detected only in embayment sediments at concentrations comparable to heavily urbanized and industrialized sediments worldwide. Planning Documents: Bight23SedQualityQAPlan Bight23FieldManual_v3_Appx_A-L Bight23SedQualityIMPlan Assessment Reports: Bight'23 Sediment Chemistry南加州湾2023年区域监测计划（Bight '23）是1994年启动、此后每五年开展一次的系列区域海洋监测工作的第七期项目。本报告呈现了本次调查的沉积物化学组分成果，该组分是Bight '23计划沉积物质量要素的组成部分之一。沉积物化学组分聚焦两个核心研究问题：（1）南加州湾（SCB）内沉积物化学暴露的范围与程度如何？（2）南加州湾内沉积物化学暴露的范围与程度随时间如何变化？ 本次研究采用分层随机抽样方案，共涵盖10个分层，包括3个大陆架水深分层（近岸：5~30米、中陆架：30~120米、外陆架：120~200米）、上陆坡（200~500米）、下陆坡（500~1000米）、海峡群岛海域（30~120米），以及4个海湾分层（游艇码头、港口、海湾与河口）。2023年7月至10月间共完成340个站位的样品采集。 沉积物样品的检测指标包括粒度、总有机碳、总氮、15种痕量金属、多环芳烃（PAHs，24种化合物总量）、多氯联苯（PCBs，43种同系物总量）、二氯二苯三氯乙烷类化合物（DDTs）以及氯丹类化合物。此外还检测了5类新兴关注有机污染物（CECs），包括多溴二苯醚（PBDE）阻燃剂、拟除虫菊酯类化合物、新烟碱类杀虫剂、1种轮胎磨损产物（6-PPD-醌，6-PPD-quinone），以及2种全氟和多氟烷基物质（PFAS：全氟辛烷磺酸（PFOS）与全氟辛酸（PFOA））。 根据加州沉积物质量目标（SQO）评估框架，整个南加州湾约83%的海底沉积物被判定为低至极小暴露水平，仅1%属于高暴露类别。海湾区域的污染程度普遍高于远海分层。在2003年至2023年的五次监测中，符合沉积物质量目标准则的海底面积占比介于61%~83%之间；除陆坡分层外，整体虽呈现出改善趋势，但该趋势未达到统计学显著性。 本次Bight '23计划新增的检测指标包括PFAS、新烟碱类杀虫剂与轮胎磨损产物，这些物质仅在海湾沉积物中普遍检出，其浓度水平与全球其他高度城市化、工业化区域的沉积物相当。 规划文件：Bight23SedQualityQAPlan、Bight23FieldManual_v3_Appx_A-L、Bight23SedQualityIMPlan 评估报告：Bight'23 Sediment Chemistry