This thesis investigated the effects of four pharmaceuticals and personal care products (PPCPs) in benthic invertebrates. Analytical methods for their extraction and determination in water, sediment, and biota, were developed and validated. Interactions with matrix coeluents were investigated, revealing that sediment and biota extracts caused significant matrix effects, which reflected the physicochemical properties of each analyte. Effects of four PPCPs were investigated in the midge 'Chironomus tentans ' and the amphipod 'Hyalella azteca,' in water-only and spiked sediment assays. The water-only toxicity (LC50) of the four compounds investigated was 0.20 to 47.3 mg/L, with toxicity rankings of triclosan > 17[alpha]-ethinylestradiol > atorvastatin > carbamazepine. No toxic effects were detected in spiked sediments. Desorption constants of 27.1 and 112.8 L/kg (Atorvastatin), 75.6 and 236.4 L/kg (Carbamazepine), and 21.2 and 232.9 L/kg (17[alpha]-Ethinylestradiol) were calculated for 'C. tentans' and 'H. azteca,' respectively, and revealed the contribution of 'C. tentans,' via bioturbation, to the desorption of PPCPs of log KOW < 3 to overlying water. The Equilibrium Partitioning Principle was used to predict the sediment toxicity of these PPCPs, yielding concentrations at least three orders of magnitude higher than environmental concentrations. Chronic toxicity of 17[alpha]-ethinylestradiol (EE2) was investigated in life-cycle assays, and EC50 values of 1.5 mg/L ('C. tentans' emergence) and 0.36 mg/L ('H. azteca' reproduction) were calculated. Acute and chronic toxicity data were combined to calculate acute-to-chronic toxicity ratios (ACRs) for EE2 of 13 ('C. tentans') and 16 ('H. azteca'). Bioaccumulation studies were conducted with EE2, in water and spiked sediments. Hyalella azteca accumulated EE2 from water, while accumulation by 'C. tentans' was mainly from sediment, reflecting the behaviour and life history of these organisms. Binding of the biota extracts to a vertebrate estrogen receptor was confirmed using a recombinant yeast estrogen receptor assay, suggesting that trophic transfer could represent an additional source of contamination for vertebrate predators. These studies indicate that adverse effects to benthic invertebrates are unlikely to occur at environmental concentrations. Bioturbation could increase the bioavailability of PPCPs through desorption to overlying water, while sensitive vertebrate predators could be exposed to additional sources of EE2 through trophic transfer.