151. Amongst the organotins, concentrations of TBT in the sediments are used by OSPAR to assess adverse effects on biota. The potential effect on benthic fauna is therefore assessed against TBT concentrations reported by the chemistry analysis. As TBT is the most toxic organotin compound to marine fauna, this considers the worst case scenario against which conservative judgment can be made.
152. Levels of TBT recorded in sediments were <4µg / kg dw at all sites and therefore fell within Class C of the OSPAR reference levels OSPAR (2009). This is a six class (A to F) assessment scheme for TBT‐specific biological effects in dogwhelks and other gastropods. The classes are described by a coloured scale (see Table 3.9) which indicates if the Ecological Quality Objectives (EcoQOs) are met, providing an indication of the effects that concentration levels of TBT tin may have on the reproductive capability of sensitive key species (OSPAR, 2009).
Table 3.9 Assessment Classes for TBT (OSPAR, 2009). Assessment class
A B C D E F
TBT sediment (μg TBT / kg dw)
n.d. < 2
2 ‐ <50
50‐<200 200 ‐500 >500
Benthic Characterisation Report November 2013
East Anglia THREE and FOUR Offshore Cable Corridor
