via conveyor systems. When contaminated (toxic) sediments are to be removed, or large volume inland disposal sites are unavailable, dredge slurries are reduced to dry solids via a process known as dewatering. Current dewatering techniques employ either centrifuges, geotube containers, large textile based filters or polymer flocculant/congealant based apparatus. In many projects, slurry dewatering is performed in large inland settling pits, although this is becoming less and less common as mechanical dewatering techniques continue to improve. Similarly, many groups (most notable in east Asia) are performing research towards utilizing dewatered sediments for the production of concretes and construction block, although the high organic content (in many cases) of this material is a hindrance toward such ends. The proper management of contaminated sediments is a modern-day issue of significant concern. Because of a variety of maintenance activities, thousands of tonnes of contaminated sediment are dredged worldwide from commercial ports and other aquatic areas at high level of industrialization. Dredged material can be reused after appropriate decontamination. A variety of processes has been proposed and tested at different scales of application (technologies for environmental remediation). Once decontaminated, the material could well suit the building industry, or could be used for beach nourishment. Environmental impacts Dredging can create disturbance to aquatic ecosystems, often with adverse impacts. In addition, dredge spoils may contain toxic chemicals that may have an adverse effect on the disposal area; furthermore, the process of dredging often dislodges chemicals residing in benthic substrates and injects them into the water column. The activity of dredging can create the following principal impacts to the environment: Release of toxic chemicals (including heavy metals and PCB) from bottom sediments into the water column. Collection of heavy metal lead left by fishing, bullets, 98% mercury reclaimed [natural occurring and left over from gold rush era]. Short term increases in turbidity, which can affect aquatic species metabolism and interfere with spawning. Suction dredging activity is allowed only during non-spawning time frames set by fish and game (in-water work periods). Secondary impacts to marsh productivity from sedimentation and general changes in wetland chemistry after dredging. Tertiary impacts to avifauna which may prey upon contaminated aquatic organisms. Secondary impacts to aquatic and benthic organisms' metabolism and mortality Possible contamination of dredge spoils sites Changes to the topography by the creation of "spoil islands" from the accumulated spoil. Releases toxic compound Tributyltin, a popular biocide used in anti-fouling paint