Imposex - Marine online assessment tool

Since 2012, imposex occurrence has reduced and is generally below the UK target threshold which measures whether adverse effects of tributyltin occur in marine snails. The associated UK target has been met in 68% of assessments in the Greater North Sea and 89% of assessments in the Celtic Seas.

Background

UK target on organotin-specific biological effects (imposex in gastropods)

This indicator is used to assess progress against the target relevant for imposex in gastropods set out in the Marine Strategy Part One (HM Government, 2012), which requires that adverse effects due to contaminant exposure are below agreed OSPAR Environmental Assessment Criteria. Meeting this Criteria for imposex in gastropods protects the marine environment from significant impacts due to the anti-foulant biocide tributyltin.

Key pressures and impacts

The key pressure associated with this indicator is the widespread use of tributyltin-based anti-fouling paints before 2008 to prevent the growth of marine organisms on ships and marine structures. Due to its high persistence, tributyltin remains in marine sediments. Tributyltin can cause imposex in marine molluscs resulting in reduced reproductive performance. This pressure has reduced significantly in recent years.

Measures taken to address the impacts

Bans on the use of tributyltin anti-foulants on boats less than 25 meters long started in the 1980s, and a global ban for all ships came into effect in 2008, when stringent European Environmental Quality Standards (European Commission, 2008) for water quality were also published. Robust controls on dredging and spoil disposal have also reduced risks from tributyltin. However, most of the tributyltin entered the sea before many of these controls were put in place and due to its persistence, it is still present. Removing contaminated sediments from the sea is not considered to be a practicable option.

Monitoring, assessment and regional co-operation

Areas that have been assessed

Status and trend assessments were conducted for the UK-portion of the Greater North Sea and Celtic Seas Marine Strategy Framework Directive sub-regions, and at the smaller scale of the 8 UK biogeographic marine regions set out in Charting Progress 2 (UKMMAS, 2010).

Monitoring and assessment methods

National risk-based imposex monitoring began in 1992, taking place at approximately 3-yearly intervals. Monitoring and assessments use methods and principles set out in the OSPAR Co-ordinated Environmental Monitoring Programme.

Assessment thresholds

Environmental Assessment Criteria for imposex measurements in a variety of gastropods have been developed by OSPAR to assess whether significant harm is occurring. OSPAR also has an aspirational ultimate objective to achieve close to background levels of effect and has developed Background Assessment Criteria related to imposex. Whilst not a target described in the UK Marine Strategy Part One (HM Government, 2012) this assessment also examines progress towards this objective.

Regional co-operation

The UK played an important role in the development, monitoring and assessment of the OSPAR “imposex in dog whelks” common indicator (OSPAR Commission, 2005; 2006). The UK results have been used in the latest OSPAR Intermediate Assessment (OSPAR Commission, 2017).

Further information

Key pressures and impacts

The key pressures associated with this indicator are anti-fouling paints, which are widely used on vessels of all sizes to prevent the growth of marine organisms. Around the beginning of the 1970s, tributyltin began to be used as the active biocide in anti-foulant paints. This compound proved extremely effective at preventing the attachment of algal and other organisms. In early uses tributyltin was “freely associated” with the paint and rapidly leached into the environment. Later paints were self-polishing, with the tributyltin bonded to the paint matrix and becoming effective as the paint surface was worn away. However, by the early 1980s oyster growers in France and the UK were becoming extremely concerned about poor growth in their stocks. Oysters were, for instance, misshapen and contained little meat, so were not marketable. The cause was the impact of tributyltin in anti-fouling paints applied mainly to pleasure vessels used in estuaries and moored in marinas close to the commercial shellfish beds. Tributyltin is toxic to many marine organisms at very low concentrations. Tributyltin is unequivocally linked to impairment of reproductive performance in several molluscan species, with some female marine snails (gastropods) developing male sex characteristics in response to tributyltin exposure (Figure 1). This is termed imposex. Tributyltin ultimately affects many organisms, but marine gastropods are among the most sensitive, making them important indicator species.

Figure 1. An affected female dog whelk Photo by Manuel Nicolaus, Cefas.

Imposex has been found to be one of the most sensitive indicators of environmental tributyltin exposure. Evidence that the development of imposex was linked to tributyltin exposure started to emerge in the 1980s (Waldock and others, 1988). In dog whelk (Nucella lapillus), the effect is dose related and severe imposex can lead to sterility in females and detrimental reproductive effects on both individuals and populations. The process and characterisation of imposex has been well documented, see, for example, Gibbs and others (1987), Oehlmann and others (1991), and Santos and others (2002). As dog whelks have limited mobility and lack a pelagic lifestage they are particularly prone to localised extinctions in the event of reproductive failure, and extinct populations may take a prolonged period to re-establish once effective measures are in place. Dog whelk monitoring is an established biological effects monitoring tool used by many OSPAR Contracting Parties (OSPAR Commission, 2013).

Legislation has been introduced over the last two decades, firstly to control the use of tributyltin-based anti-fouling paints on yachts and, more recently, the prohibition of the use of these biocides on large ships. Large-scale surveys of imposex in gastropods from across the North Sea were undertaken in 1992 and 1998 to 1999 (Minchin and others, 1999) and of the Celtic Seas in 1997 (Harding and others, 1998). In 2003, the International Maritime Organisation introduced legislation banning the application of organotin onto all ships. As sea-going vessels may be repainted with anti-fouling paint only every 5 years, this ban was extended to the presence of tributyltin on all vessels by 2008. UK National surveys conducted in 2000-2001, 2004, 2007, 2010 and 2014 span the period before, during and after the implementation of the International Maritime Organisation worldwide ban on the use and application of tributyltin anti-fouling paints on all commercial shipping, and therefore serve as a time series allowing us to measure the effectiveness of the legislation.

Measures taken to address the impacts

Over the past decades, a range of national and international legislation (measures) resulted in a continuous phase-out of tributyltin -containing paints within the OSPAR area. A global ban on tributyltin in anti-fouling systems on large vessels came into effect in 2008, when stringent new Environmental Quality Standards for water quality were also published under the European Water Framework Directive (European Commission, 2000).

UK regional co-operation to monitor and assess tributyltin effects on gastropods

The UK has worked within the OSPAR Convention to develop and implement the Joint Assessment and Monitoring Programme. This includes monitoring, assuring analytical quality and assessing the effects of tributyltin on gastropods. Assessment criteria in the form of Background Assessment Criteria and Environmental Assessment Criteria have been derived by OSPAR for imposex measurements in a variety of gastropods that represent the most sensitive species. The severity of imposex is described using the Vas Deferens Sequence Index in which the observed severity of imposex is scored for each female snail in a sample of 40 individuals and the average stage of imposex development determined for the site. Vas Deferens Sequence Index values below Background Assessment Criteria indicate a very small level of imposex in the more sensitive gastropod species. Values above Environmental Assessment Criteria indicates a risk of adverse effects such as reduced growth and recruitment, potentially leading to localised extinction. Responses between Background Assessment Criteria and Environmental Assessment Criteria are above background but are not expected to have long-term exposure effects to tributyltin.

Monitoring and assessment methods

Monitoring of imposex in dog whelks is conducted on a three-year cycle within the Clean Seas Environmental Monitoring Programme. Originally, the number of sites was extensive because all ports, harbours and marinas were probable sources of tributyltin contamination but recently the number of monitored sites has been reduced as the pressure on the environment from tributyltin releases has decreased. The most recent survey (in 2014) focussed on comparatively few stations based on those that in the previous survey in 2010 still had evidence of relatively high impacts (where Vas Deferens Sequence Index values were above or close to the Environmental Assessment Criteria. Assessments of status and trends for individual stations were conducted following standard OSPAR procedures and trend modelling comparisons of Vas Deferens Sequence Index data with Background Assessment Criteria and Environmental Assessment Criteria values (for example, see OSPAR Commission, 2017).

Assessment method

At each sampling site, up to 100 dog whelks were collected from the foreshore between spring low water and mid tide levels (Nicolaus and Barry, 2015). The location of the site was recorded using national grid references in the early survey years and in latitude and longitude using the Global Positioning System (GPS) in more recent years. Date and time of collection were also recorded for ICES reporting purposes. From the 100 animals collected, 50 specimens (young adults, with toothed shells) were taken back to the laboratory for analysis. Animals with worn shells were excluded from the sample as they could be older than 4 years.

Of the 50 individuals brought back from the shore, 40 were chosen at random and analysed. If an individual was parasitized or dead, it was excluded from the analysis and a fresh dog whelk was added. Prior to the analysis, the length of each dog whelk was measured to the nearest 0.01mm with Vernier callipers and then cracked open with a vice for further analysis, which included sex determination according to Fioroni and others (1991) and Gibbs and others (1987), penis length measurements in males and females (if present) and the associated imposex stage in females (Vas Deferens Sequence stages; Table 1). To identify the stages of imposex, the methods described by Gibbs and others (1987) were used.

After all the individuals were measured, the Vas Deferens Sequence Index was calculated as the mean of the Vas Deferens Sequence stages observed in one sample and used to assess if the Background Assessment Criteria or Environmental Assessment Criteria was breached at a specific site.

Table 1. Interpretations of the OSPAR assessment classes, referring to dog whelk (Nucella lapillus) (OSPAR Commission, 2013). VDSI = Vas Deferens Sequence Index, the Environmental Assessment Criteria (EAC) is 2 and the Background Assessment Criteria (BAC) is 0.3.

*Nucella lapillus* Vas Deferens Sequence Index (VDSI)	Effects and Impacts
VDSI ≤0.3 (BAC = 0.3)	The level of imposex in the more sensitive gastropod species is close to zero (0 – approximately 30% of females have imposex) indicating exposure to tributyltin concentrations close to zero, which is the objective in the OSPAR Hazardous Substances Strategy.
2.0	The level of imposex in the more sensitive gastropod species indicates exposure to tributyltin concentrations below the Environmental Assessment Criteria derived by OSPAR for tributyltin (approximately 30- 100% of the females have imposex). Adverse effects in the more sensitive taxa of the ecosystem caused by long-term exposure to tributyltin are predicted to be unlikely to occur.
VDSI = 2.0 - <4.0 (EAC = 2.0)	The level of imposex in the more sensitive gastropod species indicates exposure to tributyltin concentrations higher than the Environmental Assessment Criteria derived for tributyltin (there is a risk of adverse effects, such as reduced growth, and recruitment, in the more sensitive taxa of the ecosystem caused by long-term exposure to tributyltin).
VDSI = 4.0 - 5.0	The reproductive capacity in the populations of the more sensitive gastropod species, such as Nucella lapillus, is affected as a result of the presence of sterile females, but some reproductively capable females remain (there is evidence of adverse effects, which can be directly associated with the exposure of tributyltin).
VDSI = >5.0	Populations of the more sensitive gastropod species, such as Nucella lapillus, are unable to reproduce. The majority, if not all females within the population have been sterilised.
VDSI= -	The populations of the more sensitive gastropod species, such as Nucella lapillus, are absent or expired.

Assessing environmental status and temporal trends

A time series of Vas Deferens Sequence measurements concentrations is assessed for status if

there is at least one year with data in the period 2010 to 2015
there are at least 3 years of data over the time series

A time series is also assessed for trends if:

there are at least 3 years of data with individual measurements or 4 years of data with pooled measurements.

All monitoring stations where there are individual time series assessments of trend or status for Vas Deferens Sequence are shown in Figure 2.

Figure 2. Trend and status monitoring stations used to assess tributyltin effects in dog whelk.

Areas that have been assessed

Monitoring of tributyltin effects in dog whelk (Nucella lapillus) was carried out at 92 intertidal stations (Table 2) and data were assessed on a station by station basis. The results of individual stations were aggregated to give an indication of imposex levels within the 8 biogeographic regions used in Charting Progress 2 (UKMMAS, 2010a) and the two UK Marine Strategy Framework Directive regions (Greater North Sea and Celtic Seas).

Table 2. Number of time series in each biogeographic region used in the assessment of status and tends. MSFD – Marine Strategy Framework Directive

MSFD sub-Region	UK marine region	Trend assessment	Status assessment
Greater North Sea	Northern North Sea	15	15
	E Channel	4	4
Celtic Seas	W Channel and Celtic Sea	20	20
	Irish Sea	30	30
	Minches and W Scotland	19	19
	Scottish Continental Shelf	22	22

Assessment thresholds

The scale of effect was assessed against internationally agreed assessment criteria and any significant trends were identified. Vas Deferens Sequence Index values below Background Assessment Concentration (Table 1) are deemed to have a very small level of imposex in the more sensitive gastropod species. Vas Deferens Sequence Index values above Environmental Assessment Criteria indicate unacceptable levels of imposex and exposure to tributyltin, implying that there is a risk of adverse effects such as reduced growth and recruitment all the way up to extinction. Concentrations between Background Assessment Concentration and Environmental Assessment Criteria are above background but are not expected to have long-term exposure effects to tributyltin.

Results

Findings in the 2012 UK Initial Assessment

In the UK Marine Strategy Part One (HM Government, 2012), we reported that there had been a fall in the severity of imposex in dog whelks in some areas based on the evidence in the Charting Progress 2 Feeder Report on Clean and Safe Seas (UKMMAS, 2010b).

Latest findings

Status assessment

The mean concentrations across the monitoring stations used were below the Environmental Assessment Criteria values for imposex in the Celtic Seas and the Greater North Sea, and in 5 of the 6 UK biogeographic regions that were monitored (Figure 3). In the Eastern Channel, the mean value exceeded the Environmental Assessment Criteria. The percentage of individual monitoring stations, which were significantly below the Environmental Assessment Criteria values was 89% in the Celtic Seas and 68% in the Greater North Sea, indicating that 16 stations were still failing the Environmental Assessment Criteria (Figure 4). There is high confidence in these assessments.

Trend assessment

A trend assessment of the 110 stations sampled shows improvements in the UK Greater North Sea and Celtic Seas (Figure 3). All six assessed regions showed significant downward trends. At the individual station level, not a single station showed significant upward trends (Figure 3), indicating that the measures introduced by the UK Government and International Maritime Organisation are working.

Figure 3. Assessment result for sampling stations with respect to the relevant Environmental Assessment Criteria for Vas Deferens Sequence Index> Blue: mean concentration significantly (p < 0.05) below the Background Assessment Concentration; green: mean concentration significantly (p < 0.05) below the Environmental Assessment Criteria; red: mean concentration not significantly below the Environmental Assessment Criteria. Downward triangle: mean concentration significantly decreasing (p < 0.05); circle: no significant change in mean concentration (p > 0.05).

Figure 4. Individual time series Environmental Assessment Criteria (EAC) status assessment in 6 of 8 UK biogeographic sub-regions. > Blue: mean concentration significantly (p < 0.05) below the Background Assessment Concentration; green: mean concentration significantly (p < 0.05) below the Environmental Assessment Criteria; red: estimate of mean concentration not significantly below the Environmental Assessment Criteria.

Further information

The UK target requires adverse effects due to contaminant exposure to be below agreed OSPAR Environmental Assessment Criteria. Imposex is an adverse effect occurring in gastropods exposed to organotin compounds, particularly tributyltin. Meeting the Environmental Assessment Criteria for imposex in gastropods protects the marine environment from the harmful effects of tributyltin.

In the UK Marine Strategy Part One (HM Government, 2012), we reported that there had been reduced development of imposex in dog whelks from some areas based on the evidence in the Charting Progress 2 Feeder Report on Clean and Safe Seas (UKMMAS, 2010b), which looked at the trends in the various surveys since 1992. Since then, we have carried out a further 5 surveys, targeted particularly at those sampling sites where tributyltin was still being found.

A trend assessment of 110 stations (Table 3, Figures 5 and 6) showed improvements in dog whelk imposex (Vas Deferens Sequence Index) scores for the UK Greater North Sea and Celtic Seas. The regional trend assessment demonstrates improving trends in the Northern North Sea, Eastern Channel, Irish Sea, Western Channel and Celtic Sea, Minches and West Scotland, and the Scottish Continental Shelf. No regional trend assessment could be carried out for the other 2 UK biogeographic regions as insufficient stations were sampled or they do not have shorelines to provide dog whelk habitat.

Table 3. Number of time series with each trend and status by biogeographic region and Marine Strategy Framework Directive sub-region

Marine Strategy Framework Directive sub-region	Biogeographic region	Trend assessment	Vas Deferens Sequence	Status Assessment	Vas Deferens Sequence
Greater North Sea	Northern North Sea	upward trend	0	blue	2
		no trend	13	green	9
		downward trend	2	red	4
	E Channel	upward trend	0	blue	0
		no trend	4	green	2
		downward trend	0	red	2
	total	upward trend	0	blue	2
		no trend	17	green	11
		downward trend	2	red	6

Celtic Seas	Scottish Continental Shelf	upward trend	0	blue	7
		no trend	7	green	13
		downward trend	15	red	2
	Minches and W Scotland	upward trend	0	blue	1
		no trend	19	green	16
		downward trend	0	red	2
	Irish Sea	upward trend	0	blue	14
		no trend	18	green	13
		downward trend	12	red	3
	W Channel and Celtic Sea	upward trend	0	blue	7
		no trend	20	green	10
		downward trend	0	red	3
	total	upward trend	0	blue	29
		no trend	64	green	52
		downward trend	27	red	10

Figure 5. Trends for individual sites in the 6 UK biogeographic sub-regions for which sufficient data are available to assess. Most sub-regions show static trends (circles) and downward trends (downward triangles).

Figure 6. Trend assessment for imposex in dog whelk aggregated to the UK marine biogeographic regions. All sub-regions show downward trends (indicated by downward triangles).

Status assessments were also carried out for 110 stations and 6 UK marine biogeographic regions. Currently, only 16 stations have imposex responses above the Environmental Assessment Criteria (Table 4). 50% of stations in the Eastern Channel region were not significantly below the Environmental Assessment Criteria (Figure 7, Table 3). It should be noted, however, that the estimate of regional status for the Eastern Channel is more uncertain than other regions as there are only 4 sampling stations (compared to 15 or more in other assessed regions), and only one of these sites is (very slightly) above the Environmental Assessment Criteria (Figure 8).

Figure 7. Status assessment for imposex relative to Environmental Assessment Criteria (EAC) at each dog whelk sampling station. Red: Vas Deferens Sequence (VDS) not significantly below the Environmental Assessment Criteria, green: Vas Deferens Sequence significantly below Environmental Assessment Criteria but not significantly below Background Assessment Criteria; blue: Vas Deferens Sequence significantly below Background Assessment Criteria.

Figure 8. Assessment of imposex status in dog whelk for each of the UK marine regions. Red:- Vas Deferens Sequence (VDS) not significantly below the Environmental Assessment Criteria (EAC); green: Vas Deferens Sequence significantly below Environmental Assessment Criteria but not significantly below Background Assessment Concentration.

Table 4. Stations where the Vas Deferens Sequence Index for dog whelks was not significantly below the Environmental Assessment Criteria.

Station	Marine Strategy Framework Directive region	Biogeographic region
EastChan_Esussex_sh01	Greater North Sea	E Channel
EastChan_Solent_sh02	Greater North Sea	E Channel
EScotland_UgieEstBuchanN_sh01	Greater North Sea	Northern North Sea
EShetland_BressaySound_sh04	Greater North Sea	Northern North Sea
Forth_LeithDocksPortSeton_sh02	Greater North Sea	Northern North Sea
MorayF_Rosehearty_sh01	Greater North Sea	Northern North Sea
IrishSea_ArdsPenninsula_sh02	Celtic Seas	Irish Sea
IrishSea_BelfastLoughOutr_sh05	Celtic Seas	Irish Sea
IrishSea_MorecambeBay_sh03	Celtic Seas	Irish Sea
MinchMalin_SoundOfSleat_sh04	Celtic Seas	Minches and W Scotland
MinchMalin_StornowayHarbr_sh01	Celtic Seas	Minches and W Scotland
Severn_CarmarthB_sh02	Celtic Seas	W Channel and Celtic Sea
Severn_LandsTrev_sh05	Celtic Seas	W Channel and Celtic Sea
Severn_Spembrok_sh03	Celtic Seas	W Channel and Celtic Sea
WShetland_SullomVoe_sh06	Celtic Seas	Scottish Continental Shelf
WShetland_SullomVoe_sh07	Celtic Seas	Scottish Continental Shelf

Due to significant inputs of tributyltin prior to the ban on tributyltin anti-foulants, the Shetland Oil Terminal Environmental Advisory Group established an intensive biennial monitoring programme in Sullom Voe and Yell Sound (West Shetland) in 1987. Since the tributyltin ban was implemented, there has been a dramatic improvement in both the Vas Deferens Sequence Index scores across the area and in dog whelk abundance at the most impacted sites (Gubbins and others, 2010). Only one of the 20 sites had Vas Deferens Sequence Index scores above the Environmental Assessment Criteria in each of the last 2 surveys (Moore and Gubbins, 2015), which may indicate that tributyltin in contaminated sediments is occasionally bioavailable (Gubbins and others, 2012).

Dog whelks were absent at least 3 of the sites due to be surveyed for imposex in 2014: Mallaig Harbour (West Scotland), Sandhaven East (North East Scotland) and East Cowes (Eastern Channel). These sites were selected for sampling because their 2010 assessment result was above the Environmental Assessment Criteria. The situation at Mallig Harbour had been improving, while there was no trend of improvement at Sandhaven East. If dog whelk extinction is a result of tributyltin exposure, then the site is scored as “-” (see Table 1). This classification cannot be modelled in the assessment of Vas Deferens Sequence Index. The Sandhaven East site had a Vas Deferens Sequence Index score of approximately 4 in 2004, 2005, 2007 and 2010, so it is possible that tributyltin exposure has contributed to the local extinction of dog whelks at this site. Conversely, another site, the Bill of Portland station, was classed as extinct in 1997 but recovered strongly in the following years to a VDSI Vas Deferens Sequence Index score 0.46 in 2010 (Nicolaus and Barry, 2015).

The assessments of the UK marine regions, and the detailed studies at the Sullom Voe oil terminal, indicate a considerable improvement in the reproductive status of dog whelks following the ban on tributyltin-based anti-foulant paints, and that the measures implemented to control this pressure have been effective. Dog whelks are still significantly exposed to tributyltin at only a very limited number of sites, possibly because of disturbance to contaminated sediments. Only one UK region (Eastern Channel) does not meet the Marine Strategy Framework Directive target for this indicator, and the level of observed imposex is significantly decreasing there, indicating that the site is progressing to good status.

Conclusions

Since the UK Initial Assessment (HM Government, 2012), the levels of imposex in dog whelks have continued to fall. The UK Marine Strategy Part One (HM Government, 2012) target for this indicator has been met in the Celtic Seas (89% of stations) and largely met in the Greater North Sea where 68% of sampling stations exhibit no harmful effects and the severity of the response is decreasing.

Further information

The most recent surveys indicate that the Vas Deferens Sequence Index values continued to fall, with a few stations not already below the Environmental Assessment Criteria and only the Eastern Channel region subject to harmful effects of tributyltin, although the severity of the response is decreasing. With reducing trends, many sampling stations and regions already below Environmental Assessment Criteria, and a good coverage of sites there is a high level of confidence in the overall assessment. A limited number of sites show continued harm due to the presence of tributyltin and should continue to be monitored to investigate whether the existing measures need stronger local enforcement, or whether there may be alternative sources of tributyltin that need to be investigated.

Knowledge gaps

It is still unclear why occasional non-compliant samples occur in areas where this would not be expected (suggesting potential illegal use of tributyltin), and experts will investigate such cases so that appropriate action can be taken.

Further information

The extensive monitoring of imposex in dog whelks over the last 2 decades has shown that the measures taken to ban the use of tributyltin anti-fouling paints has led to clear reductions of impact. Currently, the only source of tributyltin in the marine environment is from historical or residual contamination in sediments in estuaries and harbours and arising from dredged material disposal, but this activity is tightly controlled and is unlikely to be a significant source of contamination in the future. However, it is still unclear why occasional non-compliant samples occur in areas where the effects would not be expected. Experts are investigating the possible reasons why this may be happening, such as the illegal use of tributyltin anti-fouling paint.

References

European Commission (2000) ‘Directive 2000/60/EC of the European Parliament and of the Council establishing a framework for the Community action in the field of water policy’ Official Journal of the European Union L 327, 22.12.2000, pages 1–73 (viewed on 16 November 2018)

European Commission (2008) ‘Directive 2008/105/EC of the European Parliament and of the Council of 16 December 2008 on environmental quality standards in the field of water policy, amending and subsequently repealing Council Directives 82/176/EEC, 83/513/EEC, 84/156/EEC, 84/491/EEC, 86/280/EEC and amending Directive 2000/60/EC of the European Parliament and of the Council’ (viewed on 29 November 2018)

Fioroni P, Oehlmann J, Stroben E (1991) ‘The pseudohermaphroditism of prosobranchs; morphological aspects’ Zoologischer Anzeiger, 226: 1-26 (viewed on 13 December 2018)

Gibbs PE, Bryan GW, Pascoe PL, Burt GR (1987) ‘The use of Dog-Whelk Nucella lapillus, as an indicator of Tributyltin (TBT) contamination’ Journal of Marine Biology Association of the UK, 67:507-523 (viewed on 13 December 2018)

Gubbins MJ, Devalla S, Betts T, Robinson CD (2012) ‘Concentrations of organotins in Sullom Voe sediments’ Report to SOTEAG from Marine Scotland Science, 8pages.

Gubbins MJ, Moore J, Fryer R, Davies IM (2010) ‘Long time series data showing recent recovery of gastropod populations from effects of tri-butyl tin at the Shetland Oil Terminal’ Proceedings of the ICES Annual Science conference, 20-24 September 2010, Nantes, France 12 pages (viewed on 13 December 2018)

Harding MJC, Davies IM, Minchin A, Grewar G (1998) ‘Effects of TBT in Western coastal waters’ PECD CW0691, Start date 1 February 1997, End date 28 February 1998, Fisheries Research Services number 5/98, May 1998 report 11/99 Marine Scotland Science, Aberdeen, UK (viewed on 4 January 2019)

HM Government (2012) ‘Marine Strategy Part One: UK Initial Assessment and Good Environmental Status’ (viewed on 16 November 2018)

Minchin A, Davies IM, Pymm H, Grewar GN (1999) ‘The North Sea Imposex Survey: CW0825 August 1998 - July 1999 – final report Fisheries Research Services report 11/99’ Marine Scotland Science, Aberdeen, UK (viewed on 13 December 2018)

Moore JJ, Gubbins MJ (2015) ‘Surveys of dogwhelks Nucella lapillus in the vicinity of Sullom Voe, Shetland’ July 2015, A report to SOTEAG from Aquatic Survey & Monitoring Ltd, Cosheston, Pembrokeshire and Marine Scotland Science, Aberdeen (viewed on 13 December 2018)

Nicolaus EEM, Barry J, (2015) ‘Imposex in the dogwhelk (Nucella lapillus): 22-year monitoring around England and Wales’ Environmental Monitoring and Assessment, 187:736pp (viewed on 13 December 2018)

Oehlmann J, Stroben E, Fiorini P (1991) ‘The morphological expression of imposex in Nucella lapillus (Linnaeus) (Gastropoda: Muricidae)’ Journal of Molluscan Studies, 57:375-390 (viewed on 13 December 2018)

OSPAR Commission (2005) ‘North Sea Pilot Project on Ecological Quality Objectives - Background Document on the Ecological Quality Objective on imposex in dog whelks’ Publication number: 247/2005 (viewed on 13 December 2018)

OSPAR Commission (2006) ‘Report on North Sea Pilot project on Ecological Quality Objectives’ Publication Number: 239/2006 (viewed on 13 December 2018)

OSPAR Commission (2013) ‘Background document and technical annexes for biological effects monitoring’, Update 2013 Publication Number: 589/2013 (viewed on 13 December 2018)

OSPAR Commission (2017) ‘Intermediate Assessment 2017’ (viewed on 16 November 2018)

Santos MM, ten Hallers-Tjabbes CC, Vieira N, Boon P, Porte C (2002) ‘Cytochrome P450 differences in normal and imposex-affected female Buccinum undatum from the open North Sea’’ Marine Environmental Research, 54:3-5 (viewed on 13 December 2018)

UKMMAS (2010a) 'Charting Progress 2: An assessment of the state of the UK seas' Published by Defra on behalf of the UK Marine Monitoring and Assessment Strategy community. (Viewed on 4 January 2019)

UKMMAS (2010b) ‘Charting Progress 2 Feeder report: Clean and Safe Seas’ Editors: Law, R and Maes T) Published by Department for Environment Food and Rural Affairs on behalf of the UK Marine Monitoring and Assessment Strategy committee, 366 pages (viewed on 13 December 2018)

Waldock MJ, Waite ME, Thain JE (1988) ‘Inputs of TBT to the marine environment from shipping activity in the UK’ Environmental Technology Letters, 9: 999–1010 (viewed on 13 December 2018)

Acknowledgements

Assessment metadata

Assessment Type	UK Marine Strategy Framework Directive Indicator Assessment
	D8
	D8.2 Effects of Contamination
	Marine Strategy Part One
Point of contact email	marinestrategy@defra.gov.uk
Metadata date	Saturday, September 1, 2018
Title	Organotin-specific biological effects (imposex in gastropods)
Resource abstract	Since 2012, imposex occurrence has reduced and is generally below the UK target threshold which measures whether adverse effects of tributyl tin occur in marine snails.
Linkage	Please see links provided in ‘References’ section above.
Conditions applying to access and use	© Crown copyright, licenced under the Open Government Licence (OGL).
Assessment Lineage	The 2016 assessment of the UK's Clean Seas Environment Monitoring Programme described the status and trends of contaminant concentrations and biological effects measurements in biota and sediment at monitoring stations in waters around the UK. Assessments were made for a large number of time series, typically each of a single contaminant in a single species (for biota) at a single monitoring station. The results of the individual time series at coastal and offshore stations were synthesised to assess status and trends at the biogeographic regional level and formed the basis of this indicator. Data were submitted to the MERMAN database from relevant Competent Monitoring Authorities. A series of templates were populated by submitting officers and submitted to the database which has in-built data restrictions and a data filter to ensure high quality, accurate data are submitted. The data filter has formulae in-built which use Accredited Quality Control information from known standards, limits, standard deviations and/or inter laboratory calibration exercises to calculate a score. Only data that passed a threshold agreed with the national advisory bodies were used for assessments. The data for 1999 - 2015 were extracted from MERMAN. Further data checks were made and records with obvious errors were deleted or corrected. The data were grouped into time series of VDS in a single species at a single monitoring station. Time series with no data for the period 2010 - 2015 were excluded. The individual time series were assessed for both trends and status. The methods behind the assessments and the individual time series results are available from the British Oceanographic Data Centre. The results of the individual time series at coastal and offshore stations were then synthesised to assess status and trends at the biogeographic regional level. The methods and results are available from the British Oceanographic Data Centre.
Dataset metadata	http://portal.oceannet.org/portal/start.php#details?tpc=012_Marine_Scotland_FishDAC_12111
Dataset DOI	http://dx.doi.org/10.7489/12111-1

The Metadata are “data about the content, quality, condition, and other characteristics of data” (FGDC Content Standard for Digital Geospatial Metadata Workbook, Ver 2.0, May 1, 2000).

Metadata definitions

Assessment Lineage - description of data sets and method used to obtain the results of the assessment

Dataset – The datasets included in the assessment should be accessible, and reflect the exact copies or versions of the data used in the assessment. This means that if extracts from existing data were modified, filtered, or otherwise altered, then the modified data should be separately accessible, and described by metadata (acknowledging the originators of the raw data).

Dataset metadata – information on the data sources and characteristics of data sets used in the assessment (MEDIN and INSPIRE compliance).

Digital Object Identifier (DOI) – a persistent identifier to provide a link to a dataset (or other resource) on digital networks. Please note that persistent identifiers can be created/minted, even if a dataset is not directly available online.

Indicator assessment metadata – data and information about the content, quality, condition, and other characteristics of an indicator assessment.

MEDIN discovery metadata - a list of standardized information that accompanies a marine dataset and allows other people to find out what the dataset contains, where it was collected and how they can get hold of it.

Recommended reference for this indicator assessment

E.E. Manuel Nicolaus¹, Craig D. Robinson² and Rob Fryer² 2018.Time trend and status for organotin-specific biological effects (imposex in gastropods). UK Marine Online Assessment Tool, available at: https://moat.cefas.co.uk/pressures-from-human-activities/contaminants/imposex/

¹Centre for Environment, Fisheries and Aquaculture Science

²Marine Scotland