Characterization of groundwater monitoring wells in a surficial estuarine aquifer: Using non-target analysis to develop a better understanding of the pollution sources in the biscayne bay watershed.

Biscayne Bay, a key resource for South Florida, relies on freshwater inputs to preserve the conditions necessary for a healthy ecosystem. Groundwater in Miami-Dade County (MDC) has an influential role in the watershed and acts as a contributor of freshwater to the Bay with potential anthropogenic implications. MDC is heavily urbanized, and the influence of anthropogenic activity has led to a decline in water quality, partially due to an overabundance of the limiting nutrient, phosphorus, alongside other anthropogenically-sourced contaminants. A comprehensive study was designed using ICP-QQQ-MS, HPLC-HRMS, and HPLC-MS/MS to confirm previously reported values of phosphorus contamination, identify additional contaminant relationships through non-target analysis (NTA), and quantify known wastewater tracers such as sucralose and caffeine. High concentrations of phosphorus were found at all sites, with an average of 401 ± 411 μg/L. Thirteen unique organic contaminants belonging to a variety of compound classes were identified by NTA, with PPCPs as the most common occurrence. The concentrations of sucralose ranged from 29.3 to 2070 ng/L, with an average of 535 ± 572 ng/L. Caffeine concentrations ranged from 14.4 to 1050 ng/L, with an average of 98.4 ± 226 ng/L. Significant correlations were found only between phosphorus, caffeine, and the number of 2b compounds detected by NTA. This could indicate that these contaminants are originating from the same sources. This work demonstrates the necessity of comprehensive and complementary chemical analysis to understand the impact of urban development and vulnerable wastewater systems have on groundwater quality in the Biscayne Bay Watershed.