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Steel slag is being used worldwide for a variety of applications, among which underwater dyke reinforcement. In this study the leaching and bioaccumulation of 18 inorganic compounds from Basic Oxygen Furnace (BOF) steel slag, was monitored in marine experimental ecosystems (mesocosms) for 12 weeks. Triplicated mesocosms were installed at two refreshment rates, one reflecting the situation in the Oosterschelde estuary where BOF steel slag was applied, the other at a 35 times lower rate. Vanadium in both water and biota turned out to be the best tracer for the presence of BOF steel slag in the mesocosms. The mesocosm data helped to interpret the results This article is protected by copyright. All rights reserved. Accepted Articleof a 4 year field sampling program in the Oosterschelde estuary where no elevated levels of vanadium in water or biota were found near locations where steel slag was applied. Also no ecological impact could be established in the field, which was in line with the observations in the mesocosms. This study shows the added value of a tailor made mesocosm study for realistic risk assessment, and provides support for applying this tool as a basis for designing efficient field monitoring programs.

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00000International audienceIn order to increase production of bivalves in hatcheries and nurseries, the development of new technology and its integration into commercial bivalve hatcheries is important. Recirculation aquaculture systems (RASs) have several advantages: high densities of the species can be cultured resulting in a cost-effective production system; optimal temperature maximizes production and allows rapid turnover of the product; stable water quality improves growth rate and minimizes stress and potential loss by diseases. Pilot RAS systems were developed for seed rearing of oysters (Crassostrea gigas), scallops (Pecten maximus), mussels (Mytilus edulis) and clams (Ruditapes decussatus). Optimal feed addition and waste matrix were determined. Based on this, system flow rates were designed. Seed growth in the pilot RAS systems was compared at different renewal rates and with growth in flow-through systems (FTS). All four species can be reared in RAS and showed similar growth in RAS and in FTS or in RAS with a higher renewal rate. RAS can keep O2, nitrogen and pH within the desired range. Temperature was generally higher in RAS than in FTS, probably due to heat induced by the pump circulating the water. The supply of sufficient amount of food in combination with a desire to reduce the renewal rate calls for use of concentrated feed in RAS