• Latest Version, 2024 Assessment

Status and trends of Polychlorinated Biphenyls (PCBs) in biota and sediment

Polychlorinated biphenyls (PCBs) were banned in many countries in the mid-1980s. Although local problems remain, PCB concentrations in sediment and biota have decreased in most UK assessment areas. With the exception of the most toxic congener, (CB118), concentrations are below the level at which they could present an unacceptable risk to the environment. 

Background

Polychlorinated biphenyls (PCBs) are man-made chemical compounds that were banned in the mid-1980s owing to concerns about their, toxicity, persistence, and potential to bioaccumulate in the environment. Since the 1980s, global action has resulted in big reductions in releases and remaining stocks have been phased out. However, despite European and global action, releases continue through diffuse emissions to air and water from building sites and industrial materials. Remaining sources include electrical and hydraulic equipment containing PCBs, waste disposal, redistribution of historically contaminated marine sediments and by-products of thermal and chemical industrial processes. 

PCBs do not break down easily in the environment and are not readily metabolised by humans or animals. PCBs accumulate in marine animals, with greater concentrations found at higher trophic levels. PCB compounds are toxic to animals and humans, causing reproductive and developmental problems, damage to the immune system, interference with hormones, and can also cause cancer. A sub-group of PCBs is ‘dioxin-like’, meaning they are more toxic than other PCB congeners. Seven PCB congeners (including one dioxin-like PCB - CB118) were selected as indicators of wider PCB contamination due to their relatively high concentrations and toxic effects. 

Due to their persistence in the marine environment, their potential to bioaccumulate and their toxicity, monitoring of PCBs in biota and sediment are required for the UK Marine Strategy. This indicator is used to assess progress against the target set out in the UK Marine Strategy Part One (which requires that concentrations of substances identified within relevant legislation and international obligations are below levels at which adverse effects are likely to occur).  

Further information

Polychlorinated biphenyls (PCBs) (Figure a) are industrial compounds with multiple industrial and commercial uses. It has been estimated that globally 1.3 million tonnes of PCB compounds have been produced (Breivik and others, 2007). PCBs have been used as coolants and lubricants in transformers, capacitors, and other electrical equipment. PCBs have also been used in adhesives, paints, inks and as plasticisers and sealing agents in products such as rubber and especially in polyvinyl chloride plastics used to coat electrical wiring. 

Figure A. Chemical structure of polychlorinated biphenyls 

Although usage of PCBs was banned in most forms over 30 years ago (PARCOM, 2002), they still exist in old electrical equipment and environmental media to which humans can be exposed. PCBs are expected to be present in electronic waste streams from which they can leach into the environment (Menad and others, 1998; Arp and others, 2020). Humans are exposed mainly via food, mostly from contaminated animal fats. Indoor air can also contribute to human exposure. Worldwide monitoring programmes have shown that PCBs are present in most samples of human breast milk (Pietrzak-Fiecko and others, 2005; Brajenović and others, 2018) although downwards trends have been observed. 

PCBs do not burn easily and are good insulators (Bergman and others, 2012). These properties contribute greatly to PCBs having become environmental contaminants, which are regulated by the Stockholm Convention on Persistent Organic Pollutants. The chemical inertness and heat stability properties that make PCBs desirable for industry also enable PCB residues to persist in the environment for long periods and to be transported worldwide associated with particulate matter as this is dispersed through waters, precipitation, wind, and other physical forces (Jaward and others, 2004; Eckhardt and others, 2007; Gioia and others, 2008). 

Theoretically 209 individual PCB congeners can be produced, depending on the number and position of chlorine that is substituted onto the biphenyl moiety. Individual congeners are generally named according to the short-hand system Ballschmiter and Zell (1980) developed for PCB congeners. For this naming system a number from 1 to 209, often prefixed with “CB”, was applied to each congener after the congeners had been sorted based on their structural names. This system was summarized more recently by Mills, and others, 2007. The seven ICES PCBs (CB28, 52, 101, 118, 153, 138, and 180) were recommended for monitoring by the European Union Community Bureau of Reference (EC, 2001); these PCBs were selected as indicators due to their relatively high concentrations in technical mixtures and their wide chlorination range (3–7 chlorine atoms per molecule).  

Of the 209 PCB congeners, the most toxic are the so-called ‘dioxin-like’ PCBs (DL-PCBs). The DL-PCBs are the four non-ortho (CB77, 81, 126, and 169) and eight mono-ortho (CB105, 114, 118, 123, 156, 157, 167, and 189) PCBs that also have chlorines in both para and at least two meta positions. The non-ortho PCBs can obtain a planar configuration and the mono-ortho PCBs can obtain a near planar configuration. As a result, the twelve DL-PCBs are stereochemically similar to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and therefore have similar toxic and biological responses to those of dioxins (Safe and others, 1985; Kannan and others, 1989). However, they are normally found at much lower concentrations when compared to the ortho-PCBs. CB118 is the only DL-PCB routinely monitored. 

Marine sediments, in particular those with a high organic carbon content, may accumulate hydrophobic compounds like PCBs to considerably higher concentrations than surrounding waters.  

Marine mammals, occupying the upper trophic levels and possessing large lipid reserves, can accumulate high concentrations of PCBs with concentrations often exceeding the marine mammal toxicity threshold. There is little evidence that concentrations in top predators have decreased in recent years, and publications have indicated that population declines may be due to these high concentrations (Jepson and others, 2016). 

Assessment method

In assessing contaminants both ‘relative’ and ‘absolute’ aspects have been analysed: 

‘Trend assessment’ or spatial distribution assessment to focus on relative differences and changes on spatial and temporal scales – provides information about the rates of change and whether contamination is widespread or confined to specific locations; and 

‘Status’ assessment of the significance of the (risk of) pollution, defined as the status where chemicals are at a hazardous level, usually requires assessment criteria that take account of the possible severity of the impacts and hence requires criteria that take account of the natural conditions (background concentrations) and the ecotoxicology of the contaminant. For example, Environmental Assessment Criteria (EAC) are tools in this type of assessment. 

Two assessment criteria are used to assess PCB concentrations in biota and sediment: background assessment concentrations (BACs) and environmental assessment criteria (EACs) (Table a). BACs and EAC are converted to other bases (ww – wet weight, dw – dry weight or lw – lipid weight) using species-specific conversion factors (Table b). BACs are an aspirational ultimate objective to achieve the background concentrations which naturally occur in the marine environment and whilst not a UK Marine Strategy target, the status and trend results were used to examine progress towards this objective. 

Assessment method 

PCB concentrations are measured in biota (shellfish and fish) and sediment samples taken routinely (every 1 - 6 years depending on site) from monitoring sites throughout much of the UK regions (Figure 1). Additional data is available but was not included in the regional status and trend assessment due to there being too few stations or number of years. For an individual time series to be assessed for status or trends there must be at least one year with data in the period 2016 to 2021. 

Monitoring of PCBs in UK regions began in 1999. The number of time series used in each UK Region is shown in Table c. Only assessment areas with at least three monitoring sites with a reasonable geographic spread were included in the regional assessment of status and temporal trends. The regional assessment only considered coastal and offshore stations and excluded estuarine stations. 

For each PCB compound at each monitoring site, the time series of concentration measurements was assessed for trends and status using the methods described in the OSPAR Hazardous Substances Assessment Tool https://dome.ices.dk/OHAT/?assessmentperiod=2023. The results from these individual time series were then synthesised at the assessment area scale in a series of meta-analyses. The most toxic (and dioxin-like) PCB of the ICES7 PCBs (CB118) was assessed separately. 

Trend assessments included those monitoring sites that were representative of general conditions and excluded those monitoring sites impacted due to a point source as well as baseline monitoring sites where trends would not be expected. Analysis was also restricted to assessment areas where there were at least three monitoring sites with trend information and where those monitoring sites had reasonable geographic spread. The regional assessment only considered coastal and offshore stations and excluded estuarine stations. 

The trend in each congener at each monitoring site was summarised by the estimated annual change in log concentration, with its associated standard error. The annual change in log concentration was then modelled by a linear mixed model with a fixed effect: 

         ~ UK biogeographic region 

and random effects: 

         ~ congener + congener: UK biogeographic region + monitoring site + congener: monitoring site [biota only] + residual variation 

The choice of fixed and random effects was motivated by the assumption that the PCB congeners would have broadly similar trends, since they have similar sources. Thus, the fixed effect measures the common trend in PCB congeners in each OSPAR contaminants assessment area and the random effects measure variation in trends: 

• between congeners common across UK biogeographic region (congener); 

• between congeners within UK biogeographic region (congener: UK biogeographic region); 

• between monitoring sites common across congeners (monitoring site);  

• between congeners but common across tissues and species within monitoring sites (congener : monitoring site); and 

• residual variation. 

The residual variation is made up of two terms: the variation associated with the estimate of the trend from the individual time series, which is assumed known (and given by the square of the standard error); and a term which accounts for any additional residual variation not explained by the other fixed and random effects. 

Evidence of trends in PCB concentration at the assessment area scale was then assessed by plotting the estimated fixed effects with point-wise 95% confidence intervals. Differences between congeners were explored by plotting the predicted trend for each congener and for each congener / assessment area combination with point-wise 95% confidence intervals. 

Similar analyses explored status at the assessment area scale. Two summary measures were considered: the log ratio of the fitted concentration in the last monitoring year to the EAC; and the log ratio of the fitted concentration in the last monitoring year to the BAC. Impacted monitoring sites were also included in these analyses. 

Finally, concentration profiles across congeners at the assessment area scale were explored using the fitted log concentration in the last monitoring year. 

BACs and EACs are available for the following PCBs in biota (Table A). 

Table A: Background assessment criteria (BACs) and Environmental Assessment Criteria (EACs) for polychlorinated biphenyls (PCBs) in sediment and biota (fish and shellfish)

 

	BAC	BAC	BAC	EAC	EAC
	Mussels and Oysters	Fish	Sediment	all biota	Sediment
Determinant	(μg/kg dw)	(μg/kg ww)	(μg/kg dw)	(μg/kg lw)	(μg/kg dw)
CB28	0.75	0.10	0.22	67	1.7
CB52	0.75	0.08	0.12	108	2.7
CB101	0.70	0.08	0.14	121	3.0
CB105	0.75	0.08
CB118	0.60	0.10	0.17	25	0.6
CB138	0.60	0.09	0.15	317	7.9
CB153	0.60	0.10	0.19	1585	40
CB156	0.60	0.08
CB180	0.60	0.11	0.10	469	12

Table A notes: dw, dry weight; ww, wet weight; lw, lipid weight. For sediment BACs are normalised to 2.5% organic carbon; for biota BACs and EAC are converted to other bases (ww, dw or lw) using species-specific conversion factors (Table B); BACs in fish only applied to tissue / species with lipid > 3%; and the EACs are based on partitioning theory and are sometimes known as EAC^passive.   

The Maximum Permissible Concentrations (MPC, used to assess the human health status) for SCB6 concentrations (sum of CB28, 52, 101, 138, 153 and 180) is 75 and 200 μg/kg ww for fish muscle and fish liver respectively.  

Table B: Typical % dry weight (% dw) and % lipid weight (% lw) for each species and tissue. The values are derived from monitoring data for the years 2000 to 2019 inclusive based on an extraction from the ICES data base on 1 February 2021. 

species	common name	% lw in muscle	% dw in muscle	% lw in liver	% dw in liver	% lw in soft body	% dw in soft body	% lw in tail muscle	% dw in tail muscle
Clupea harengus	herring	4.6	26.6	4.4	32.0
Gadus morhua	cod	0.3	19.3	43.0	55.0
Lepidorhombus whiffiagonis	megrim	0.3	20.2	25.0	40.6
Limanda limanda	common dab	0.7	20.1	19.5	32.6
Merlangius merlangus	whiting		20.2	36.9	44.3
Merluccius merluccius	hake		20.0	43.7
Molva molva	common ling	0.3	21.1	53.0	64.2
Platichthys flesus	flounder	0.9	21.3	14.6	32.0
Pleuronectes platessa	plaice	0.5	20.0	11.4	26.7
Scomber scombrus	Atlantic mackerel		25.6	7.0	26.6
Zoarces viviparus	eelpout	0.6	18.7	0.6	22.1
Cerastoderma edule	common cockle						19.0
Mya arenaria	softshell clam					0.7	14.8
Ruditapes philippinarum	manila clam						16.0
Mytilus edulis	blue mussel					1.4	16.3
Mytilus galloprovincialis	Mediteranean mussel					2.2	19.0
Crassostrea gigas	Pacific oyster					2.1	18.0
Ostrea edulis	native oyster					1.8	20.4
Crangon crangon	common shrimp							1.4	27.3
Littorina littorea	common periwinkle						21.9
Nucella lapillus	dog whelk						32.8
Tritia nitida / reticulata	dog whelk (nitida / reticulata)						27.1
Cepphus grylle	black guillemot				32.0
Fulmarus glacialis	northern fulmar				29.4
Globicephala melas	long-finned pilot whale	70.0	29.0		27.6

The number of monitoring sites used to assess trends and status by Marine Strategy sub-region and UK biogeographic region are shown in Tables C. 

Table C: Number of monitoring sites within each Marine Strategy sub-region and UK biogeographic region used in the assessment of temporal trends and status 

		Sediment	Sediment	Biota (shellfish and fish)	Biota (shellfish and fish)
Marine Strategy sub-region	UK Region	Trends	Status	Trends	Status
Greater North Sea	Northern North Sea	11	17	19	23
Greater North Sea	Southern North Sea		8	9	10
Greater North Sea	East Channel		4	2	4
Celtic Seas	Scottish Continental Shelf			1	1
Celtic Seas	Minches and Western Scotland	5	5	3	3
Celtic Seas	Irish sea	9	17	19	25
Celtic Seas	West Channel and Celtic Sea	1	2	3	3

Differences in methodology used for the UKMS 2018 compared with the UKMS 2024 

This assessment includes the assessment of in PCBs in sediment and biota. These were assessed separately for the 2018 MS assessment. The most toxic (and dioxin-like) PCB of the ICES7 PCBs (CB118) was assessed separately in 2024. Although not presented in this assessment, the status assessment against the human health standards (QS(hh)) can be found on the OSPAR Hazardous Substances Assessment Tool https://dome.ices.dk/OHAT/?assessmentperiod=2023 

Results

Polychlorinated biphenyl (PCB) concentrations are measured in sediment, fish and shellfish, collected between 1999 and 2021 from monitoring sites throughout UK biogeographic regions (Figure 1), at frequencies ranging from annually to every six years. Only assessment areas with at least three monitoring sites and a reasonable geographic spread were included in the assessment of status and temporal. The regional assessment only considered coastal and offshore stations and excluded estuarine stations.

 

Figure 1a Monitoring sites used to assess PCB concentrations in sediment in each Marine Strategy region (dark lines) and biogeographic subregion (light lines). The filled circles indicate sites where there are sufficient data to assess both status and trends; the open circles indicate sites where only status can be assessed. There are additional sites that are not shown because they were not sampled often enough. 

Figure 1b Monitoring sites used to assess PCB concentrations in fish and shellfish in each Marine Strategy region (dark lines) and biogeographic subregion (light lines). The filled circles indicate sites where there are sufficient data to assess both status and trends; the open circles indicate sites where only status can be assessed. There are additional sites that are not shown because they were not sampled often enough. 

The data are used to investigate trends in PCB concentrations and to compare concentrations against two sets of assessment values: Background Assessment Concentrations (BACs) and Environmental Assessment Criteria (EACs). Where concentrations are below the EAC they should not cause chronic effects in sensitive marine species and so should present no significant risk to the environment. BACs are used to assess whether concentrations are close to zero for man-made substances, the ultimate aim of the OSPAR Hazardous Substances Strategy. Data for the most toxic dioxin-like PCB (CB118) were assessed separately from the other six PCB congeners (CB28, 52, 101, 138, 153, 180- ICES 6 PCBs). 

Status Assessment 

Concentrations in sediment and biota for the ICES 6 PCBs (non-planar PCBs) are above the BAC but below the EAC in all UK biogeographic regions (Figure 2). For the most toxic, dioxin-like PCB (CB118) concentrations were above the EAC for sediment in one of the four assessment areas (Irish Sea). CB118 concentrations in biota were also above the EAC in this region, and in three additional regions (Northern North Sea, East Channel and West Channel and Celtic Sea), indicating possible adverse effects on marine life in these areas.  

Figure 2a The mean concentration of the ICES 6 PCBs and of CB118 (coloured circles) in sediment in each biogeographic region relative to the Environmental Assessment Criterion (EAC). A value of 1 occurs when the mean concentration equals the EAC. The horizontal line indicates the upper one-sided 95% confidence limit on the mean. The mean concentration is significantly below the EAC (p < 0.05) if its upper confidence limit is less than 1. Dark blue: the mean concentration is significantly below the EAC (p < 0.05) but not the Background Assessment Concentration. Red: the mean concentration is not significantly below the EAC (p > 0.05). 

Figure 2b The mean concentration of the ICES 6 PCBs and of CB118 (coloured circles) in fish and shellfish in each biogeographic region relative to the Environmental Assessment Criterion (EAC). A value of 1 occurs when the mean concentration equals the EAC. The horizontal line indicates the upper one-sided 95% confidence limit on the mean. The mean concentration is significantly below the EAC (p < 0.05) if its upper confidence limit is less than 1. Dark blue: the mean concentration is significantly below the EAC (p < 0.05) but not the Background Assessment Concentration. Red: the mean concentration is not significantly below the EAC (p > 0.05). 

Trend Assessment 

For sediment only three regions were assessed for trends, concentrations were stable for both the ICES 6 PCBs (non-planar PCBs) and CB118 in all three regions (Figure 3). For biota two of the four regions (Northern North Sea and Irish Sea) assessed showed significant downwards trends for the ICES 6 PCBs and CB118 (Figure 4). CB118 also showed a significant downward trend in the Southern North Sea.  

Figure 3 The percentage annual change (circle) in the mean concentration of the ICES 6 PCBs and of CB118 in sediment in each biogeographic region. The horizontal line is the associated 95% confidence interval. There is a significant change in mean concentration (p < 0.05) if the confidence interval does not cut the vertical line at 0. The circle indicates that there is no significant change in mean concentration (p > 0.05). 

Figure 4 The percentage annual change (circle, triangle) in the mean concentration of the ICES 6 PCBs and of CB118 in fish and shellfish in each biogeographic region. The horizontal line is the associated 95% confidence interval. There is a significant change in mean concentration (p < 0.05) if the confidence interval does not cut the vertical line at 0. Circle: no significant change in mean concentration (p > 0.05). Downward triangle: significant decrease in mean concentration (p < 0.05). 

 

Further information

Regional Assessment Results 

Contamination from polychlorinated biphenyls (PCBs) is widespread and persists in the marine environment. In sediments, PCB concentrations are highest in the Irish Sea, and lowest in the Minches and Western Scotland and Northern North Sea. However, all PCBs are not yet at concentrations close to zero even at monitoring stations remote from industrial activity (Figure a). Only for one PCB congener (CB28) in two regions (Minches and Western Scotland and Northern North Sea) were concentrations in sediment close to zero. In one assessment area (Irish Sea) there are locations where concentrations of the most toxic PCB congener (CB118) pose a risk of pollution effects (>EAC). CB118 in sediment from the Irish Sea was also the only PCB to exceed the EAC in the UK Marine Strategy Framework (MSFD) assessment in 2018. 

Individual PCB concentrations in biota in UK regions areas are still above the BAC (Figure a), and concentrations for CB118 exceeded the EAC in four (Northern North Sea, East Channel, Irish Sea and West Channel and Celtic Sea) of the six regions assessed. Similarly, the UKMS1 assessment in 2018 showed that four (Northern North Sea, Southern North Sea, Irish Sea, and Scottish Continental Shelf) of the five regions assessed for PCBs in biota exceeded the EAC for CB118. In the Southern North Sea, CB118 was below the EAC in the UKMS1 2024 assessment, whilst in 2018 exceeded the EAC, showing there has been some improvement.

 

Figure Aa The mean concentration of individual PCBs (coloured circles) in sediment in each biogeographic region relative to the Background Assessment Concentration (BAC). A value of 1 occurs when the mean concentration equals the BAC. The horizontal line indicates the upper one-sided 95% confidence limit on the mean. The mean concentration is significantly below the BAC (p < 0.05) if its upper confidence limit is less than 1. Light blue: the mean concentration is significantly below the BAC (p < 0.05). Dark blue: the mean concentration is significantly below the Environmental Assessment Criterion (EAC) (p < 0.05) but not the BAC. Red: the mean concentration is not significantly below the EAC (p > 0.05). 

Figure Ab The mean concentration of individual PCBs (coloured circles) in fish and shellfish in each biogeographic region relative to the Background Assessment Concentration (BAC). A value of 1 occurs when the mean concentration equals the BAC. The horizontal line indicates the upper one-sided 95% confidence limit on the mean. The mean concentration is significantly below the BAC (p < 0.05) if its upper confidence limit is less than 1. Dark blue: the mean concentration is significantly below the Environmental Assessment Criterion (EAC) (p < 0.05) but not the BAC. Red: the mean concentration is not significantly below the EAC (p > 0.05). 

Owing to their slow breakdown in the environment, PCBs will persist in marine sediments for many years to come. However, a number of regions are showing downward trends for sediments and biota (Figure b). Sediment in the Northern North Sea showed decreasing trends for three PCB congeners (CB101, CB138 and CB180). No significant trends were seen for any of the ICES 7 PCBs in sediment in the Irish Sea and Minches and Western Scotland. Only one region did not show any decreasing trends for any of the ICES 7 PCBs in biota (West Channel and Celtic Sea). Concentrations for all ICES 7 PCBs in biota were decreasing in the Irish Sea; in the Northern North Sea only CB180 did not show a decreasing trend, and CB118 and CB28 were decreasing the Southern North Sea. 

Figure Ba The percentage annual change (circle, triangle) in the mean concentration of individual PCBs in sediment in each biogeographic region. The horizontal line is the associated 95% confidence interval. There is a significant change in mean concentration (p < 0.05) if the confidence interval does not cut the vertical line at 0. Circle: no significant change in mean concentration (p > 0.05). Downward triangle: significant decrease in mean concentration (p < 0.05). 

Figure Bb The percentage annual change (circle, triangle) in the mean concentration of individual PCBs in fish and shellfish in each biogeographic region. The horizontal line is the associated 95% confidence interval. There is a significant change in mean concentration (p < 0.05) if the confidence interval does not cut the vertical line at 0. Circle: no significant change in mean concentration (p > 0.05). Downward triangle: significant decrease in mean concentration (p < 0.05). 

Individual Time Series Results per Monitoring Site 

A summary of individual time series results at monitoring sites across the UK for PCB concentrations in sediment is presented here https://dome.ices.dk/OHAT/?assessmentperiod=2023 

In total, mean concentrations of PCBs in sediment are below the EAC in 314 out of 350 time series (90%). In 143 out of 154 time series (93%), mean concentrations have decreased or stayed stable over the assessment period. For biota, mean PCB concentrations are below the EAC in 372 out of 447 time series (83%), with concentrations staying stable or decreasing in 317 out of 322 time series (98%). For biota and sediments, CB118 was the main congener to be above the EAC. It should be noted that only individual time series results in areas with a sufficient number of stations are included in in the regional assessments (see number of time series used in each UK biogeographic region and assessment area in Table C), due to the criteria set out in the assessment methodology. 

Confidence Assessment 

There is high confidence in the quality of the data used for this assessment. The data have been collected over many years using established sampling methodologies. There is sufficient temporal and spatial coverage and no significant data gaps in the areas assessed over the relevant time periods. The synthesis of monitoring site data for the assessment area scale are based on established and internationally recognised protocols for monitoring and assessment per monitoring site, therefore there is also high confidence in the methodology. 

Conclusions

More than 30 years after polychlorinated biphenyls (PCBs) were banned, PCBs are still found in marine sediments and in biota (fish and shellfish) in the UK regions, with concentrations in some areas at levels that may cause adverse effects on marine life. 

Concentrations are decreasing in many regions, particularly for biota. With the exception of the most toxic congener (CB118), concentrations of all PCB congeners in sediment and biota are below the level at which they could present an unacceptable risk to the environment. Mean concentrations of CB118 in sediment are at or above this level in one of the four areas assessed, and for biota in four of six areas assessed. 

PCBs remain in the sediment for long periods and have the potential to accumulate in biota and biomagnify up food chains. Due to past industrial uses and the persistence of PCBs in the environment it will take several more decades before concentrations are close to zero, the ultimate aim of the OSPAR Hazardous Substances Strategy. 

Further information

Historic contamination of the environment by polychlorinated biphenyls (PCBs) means there are limited possibilities for addressing the issue of PCB concentrations in sediment and biota. 

In parallel to reduced PCB emissions in areas of former use, studies have recorded surprisingly high concentrations of PCBs in areas far from the traditional sources (Jaward and others, 2004; Gioia and others, 2008). There are indications that primary emission sources of PCBs are increasing from some African countries, where PCBs have not been commercially produced and used. Major sources of PCBs in African countries include transformers, continuing import of e-waste from other countries outside of Africa, shipwrecks, and biomass burning (Gioia and others, 2013; Akinrinade and others, 2020). 

Knowledge gaps

There is a lack of monitoring data, or insufficient data for a status and trend assessment, particularly for sediment, not all regions had sufficient number of sites for a regional assessment.  

Even with discontinued use, it is likely that polychlorinated biphenyls (PCBs) are continuing to enter the environment through secondary sources such as leachate from waste disposal sites. Further research is required to define and quantify diffuse inputs from terrestrial sources. 

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Stockholm Convention of Persistent Organic Pollutants (POPs) adopted to EU legislation in Regulation (EC) No 850/2004, amended 2009

Authors

Lynda Webster (Marine Directorate of the Scottish Government)  

Assessment Metadata

Please contact marinestrategy@defra.gov.uk for metadata information

Assessment metadata

Assessment Type
Point of contact email	marinestrategy@defra.gov.uk
Metadata date	Sunday, June 1, 2025
Title
Resource abstract
Linkage
Conditions applying to access and use
Assessment Lineage
Dataset metadata
Dataset DOI	The Scottish Government, Marine Directorate. 2025. https://doi.org/10.7489/12541-1

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.