Scottish Marine and Freshwater Science Volume 3 Number 5: SOTEAG Rocky Shore Monitoring Programme. TBT Contamination in Sullom Voe, Shetland. 2011 Dogwhelk Survey

1. Introduction

Tributyltin ( TBT) compounds have been recognised as some of the most toxic substances released into the aquatic environment. Extensive reviews have been published outlining the toxicity of TBT to aquatic organisms (e.g. Hall and Pinkney, 1985; Laughlin and Linden, 1987; Muller et al., 1989; IMO, 1989; IPCS, 1990).

Sullom Voe is a large fjordic inlet on the mainland of Shetland ( Figure 1). The mouth of the voe is approximately 5 km wide, and the voe extends approximately 13 km southwards (Dooley, 1981). A large oil terminal situated on the promontory of Calback Ness was opened in November 1978. There was a peak in the tonnage and number of crude and gas tankers visiting the terminal in 1984 and the tonnage and numbers have since fallen. There have been no fish farms within the voe, and no significant small boat activity occurs in the area. TBT contamination therefore arises from tankers (Bailey and Davies, 1988) and, up until 1986, from TBT antifoulants used on towing vessels, navigational buoys and harbour craft (Shetland Islands Ports Authority and Shetland Islands Council, pers comm, 1991). Reducing shipping traffic, a historical change from free association to co-polymer TBT based antifoulants and recent IMO restrictions on the use of TBT on large vessels (no new applications in 2003 and no exposed TBT paints on vessels in 2008) means that TBT inputs to the area from marine sources have been reducing and should now have ceased.

Extensive laboratory and field investigations have been undertaken demonstrating the occurrence of male sexual characteristics in female dogwhelks (a condition termed imposex; Blaber, 1970) resulting from exposure to TBT. The sensitivity and usefulness of using the dogwhelk as an indicator of TBT contamination is well established (e.g. Gibbs et al., 1987; Bailey and Davies, 1989) and has been included in international monitoring programmes under the Oslo and Paris Commission (Davies et al., 1997; Gubbins et al., 2004).

The following report details results of a survey that used the common dogwhelk ( Nucella lapillus L.) as an indicator of TBT contamination arising from oil terminal operations in Sullom Voe. The aim of the survey was to provide continuing comparable time series data on the effects of TBT contamination in and around Sullom Voe and, in particular, assess if the dogwhelk populations have shown any further recovery since the last survey which took place in 2009 (Gubbins, 2009).