ABSTRACT: Bulk concentrations of PTEs (potentially toxic elements) were assessed and compared with foraminiferal assemblages from core sediments from TL (Torrecillas Lagoon), on the north coast of Puerto Rico. Temporal distributions of mud, Fe, Al (proxy for terrigenous sedimentation), and rhenium (proxy for anoxia) reflected changes in land use within the drainage basin associated with human activities over the past century. The mud-dominated sediments provided a major “sink†for PTEs, while Fe oxides and sulfides served as a secondary “sinksâ€. Temporal variability of Re revealed intervals of aerobic vs anaerobic conditions in the lagoon. The dominant foraminiferal taxa, Ammonia beccarii, Quinqueloculina rhodiensis, Quinqueloculina seminula, and Ammobaculites agglutinans, coupled with low foraminiferal densities and species diversities, as well as barren samples, are characteristic of stressed estuarine environments. Overall bulk concentrations of Cu and Zn negatively correlated with foraminiferal absolute/relative abundances, diversity indices and incidences of test deformities. However, there are no correlations with the assumed bioavailable counterparts (F2Tess-Cu and F2Tess-Zn) were observed. These results indicate that fractionation of PTEs need to be considered in relation to their biological significance to foraminiferal ecology, which may differ substantially from bioavailability to metazoans that ingest sediments. The application of the acid-soluble F2Tess is not recommended in environmental studies using foraminifers as bioindicators, as PTEs in this fraction are likely not bioavailable to these protists.