A medium-term mesocosm exposure study was conducted to elucidate bioaccumulation and depuration of polychlorinated biphenyl congener 153 (PCB-153) in edible shrimp Palaemonetes varians. Over the 15-day exposure period, shrimp under different exposure concentrations exhibited a significant increase in PCB153 concentration compared with control organisms. Distinct bioaccumulation patterns and uptake rates were observed depending on the exposure concentrations. For low PCB-153 exposure levels (0.25 μg L 1), accumulation followed a saturation model, reaching an apparent steady state after fifteen days exposure. For intermediate (2.5 μg L 1) and high PCB-153 levels (25 μg L 1), accumulation was faster and linear. In addition, the bioaccumulation rate was not proportional to PCB-153 concentration, and the bioaccumulation was higher at intermediate exposure concentrations. Regarding the depuration phase, P. varians lost up to 30% of PCB-153 after 72h and levels continued slowly to decrease until the end of the 30-d experimental period. However, PCB-153 levels in shrimp did not reach background values, and those exposed to moderate and high PCB-153 concentrations presented contamination levels much higher than the regulatory limit for human food consumption (75ngg 1 ww for Σ6 PCB). ; This research was supported by FCT (Fundação para a Ciência e Tecnologia) through a PhD grantat tributed to T. F. Grilo (SFRH/BD/ 44936/2008) and MERCOAST project (PTDC/MAR/101906/2008), with funds from POPH (Portuguese Operational Human Potential Program), QREN Portugal (Portuguese National Strategic Reference Framework), and MCTES (Portuguese Ministry of Science, Technology, and Higher Education). P. Pato acknowledges a post doctoral fellowship from FCT (SFRH/BPD/35068/2007).