Man-made chemicals and heavy metals enter the Baltic Sea via numerous sources, including waste water treatment plants, leaching from household materials, leaching from waste deposits, and atmospheric deposition from industrial plant emissions, amongst others.

Photo: Cezary Korkosz
What is the status?

The pressure from contaminants is high in the entire Baltic Sea.

Among the assessed substances, PBDEs (flame retardants) and mercury (heavy metal) have particularly elevated concentrations. Several environmentally hazardous substances are currently not assessed.

Oil spills have decreased in all sub-basins of the Baltic Sea.

NOTE
This website contains the 2018 updated version of the State of the Baltic Sea report. For the first version of the report and other materials, please see the HOLAS II - First version workspace on HELCOM's website.

Man-made chemicals and heavy metals enter the Baltic Sea via numerous sources, including waste water treatment plants, leaching from household materials, leaching from waste deposits, and atmospheric deposition from industrial plant emissions, amongst others. Once in the Baltic Sea, they can cause various types of damage to the ecosystem. Some are highly visible in the form of oil-spills, others however can remain unnoticed or are only apparent when detrimental impacts on the ecosystem or biota are observed. Many contaminants degrade slowly and their impacts can magnify as they accumulate within the aquatic food web. The contamination status is elevated compared to natural conditions in all parts of the Baltic Sea.

Thousands of environmentally hazardous substances have been identified as potentially occurring in the Baltic Sea. The most harmful substances are persistent, toxic and accumulate in biota. Some hundreds of substances are regularly monitored. A subset of these are represented in the core indicators included in this assessment.

Indicators included in the assessment

The core indicators are assessed against regionally agreed threshold values (Box 4.2.1; for more details see Thematic assessment; HELCOM 2018C). These are derived from a number of sources to select values that have been scientifically tested and developed with the purpose of assessing environmental status or ensuring human safety.  However, a risk can never be fully excluded even when the threshold value is achieved – especially for persistent or bio-accumulating substances – and the long-term goal is to reach zero concentrations of man-made chemicals.

Since the previous holistic assessment, HELCOM has further developed the assessment system for hazardous substances, and taken steps towards applying regionally harmonised methods. The integrated assessment was done using the HELCOM CHASE tool, which integrates individual results for indicator substances (or substances groups) into a quantitative estimate of overall contamination status.

Box 4.2.1 Threshold values for hazardous substances

Monitoring of hazardous substances takes place in three types of matrices, namely biota, water and sediment. Each of these has specific threshold values defined for each substance (or substance group)

Integrated status assessment

Pressure on the marine environment from contaminants is high in all parts of the Baltic Sea (Figure 4.2.1). The ecosystem remains impacted by hazardous substances. Mercury, polybrominated diphenyl ethers, and the radioactive isotope cesium-137 show particularly high contamination scores in the integrated assessment.

Polybrominated diphenyl ethers (PBDEs) have mainly been used as flame retardants in plastic materials and polyurethane foams, and enter the Baltic Sea through waste water treatment plants and diffuse sources. The use of these flame retardants has been banned in most products since 2004 in Europe. The main source of heavy metals, such as mercury, is burning of fossil fuels, which enter the Baltic Sea through atmospheric deposition. Mercury is currently legally used in some applications such as low-energy light sources for example, but its use in several previous industries, including amalgams in dentistry, electrodes in paper bleaching, and thermometers, have been phased out.

Eleven of the assessed open sea areas are classified into the worst status category, with the Kiel Bay, Eastern Gotland Basin and Bothnian Bay being indicated as the most contaminated. Meanwhile, areas appearing to show better relative status are generally associated with low confidence in the assessment. The matrix ‘biota’ was commonly classified as having the worst status, and was thus a strong driver of the overall contamination status.

Figure 4.2.1. The integrated contamination status of the Baltic Sea assessed using the CHASE tool.

Figure 4.2.1. The integrated contamination status of the Baltic Sea assessed using the CHASE tool. The assessment shows that hazardous substances give cause for concern in all assessed units. The integrated assessment is based on seven core indicators integrating concentrations-to-threshold derived values (Contamination ratios) for twelve individual hazardous substances (or substance groups). The pie charts indicate how many out of the twelve substances were assessed, defining those that achieved (green) or failed (red) their respective threshold value in each of the open sea assessment units. The overall assessment is moderated by a parallel assessment of confidence (see left inset map) and can be considered as an appraisal of the data coverage and quality in any given assessment unit. For Denmark the assessments of hazardous substances have been done in accordance with the Water Framework Directive due to consideration of the national management of the coastal and territorial waters. The assessment can be found in the Danish national River Basin Management Plans.

The total range of contamination ratios for the HELCOM core indicators, by substance or substance group is shown in Figure 4.2.2 for all coastal and open sea assessment units. Those substances most distant from their threshold values and failing the threshold value (based on the whole regional scale) are PBDEs, mercury, cesium-137, as well as tributyltin (TBT) and imposex[1]. Detailed results per core indicator and substance per open sea assessment unit are presented in Figure 4.2.3.

Figure 4.2.2: Range of contamination ratios of the evaluated hazardous substances.

Figure 4.2.2. Range of contamination ratios of the evaluated hazardous substances. The contaminant ratios are the observed concentration value divided by the threshold value, based on the mean concentrations for the assessment period 2011-2016. The horizontal bars show the range of contamination ratios from percentile 20 to 75 for each substance on a log-transformed scale. Red bars indicate that the median value fails the threshold value, as identified by the green line. The figure is based on the coastal and open sea data used in the integrated assessment. In addition, corresponding results for the core indicator on tributyltin[2] and imposex, which is not used in the integrated assessment, is presented. The core indicators are presented in more detail in the Core indicator reports (HELCOM 2018s-z).

Figure 4.2.3. Detailed results for the hazardous substances assessment in the open sea assessment units, by core indicators and substances.

Figure 4.2.3. Detailed results for the hazardous substances assessment in the open sea assessment units, by core indicators and substances. Red denotes that the substance fails the threshold value, and green denotes that threshold value is achieved. White cells are shown for units not assessed due to a lack of data. The core indicators have primary and secondary substances and threshold values. Primary substances and the matrix in which the primary threshold is set are shown in bold. Secondary substances and threshold values are shown in italics. Abbreviations used for matrices: B=biota; S=Sediment, W=Water, for substances (or groups): BCDD = hexabromocyclododecane, PBDE = polybrominated diphenyl ethers, PAHs = polyaromatic hydrocarbons, PCBs = polychlorinated biphenyls, PFOS = perfluorooctane sulphonate, TBT = tributyltin. The twelve substances (or groups) used in the integrated assessment are marked with pale blue shading.

Confidence in the assessment

The integrated results for the geographical areas are regionally comparable, however the variation in confidence needs to be considered. Assessment units with lower confidence generally showed better status than those with high confidence, which can partly be attributed to the absence of monitoring of polybrominated diphenyl ethers or mercury, the two substances generally being the furthest from their respective threshold values, in these areas. Polybrominated diphenyl ethers and mercury were highly influential in areas being assessed as not achieving good status in all areas where they were monitored.

Changes in comparison to the previous assessment

The overall contamination status has not changed markedly since the previous holistic assessment (HELCOM 2010), showing that contamination from hazardous substances still gives cause for concern throughout the Baltic Sea area. Based on an analyses at core indicator level, the situation seems, however, not to be deteriorating. Out of 559 data series analysed with respect to trends over time, close to half (236) showed downward trends, 311 showed no detectable trend, and only 12 showed upward trends (Figure 4.2.4).

Due to the methodological differences between assessment periods, it is not possible to make a direct comparison between the current (2011-2016) and the previous holistic assessment. For example, there has been a development of regionally agreed threshold values, different substances or substance groups are sampled, and there is a substantial increase in the monitoring data included in the assessment. Changes can, however, be seen with respect to selected aspects. For example, polychlorinated biphenyls (commonly known as PCBs) and dioxins were identified amongst the substances having highest contamination ratios in the previous assessment (HELCOM 2010), but PCBs, dioxins and furans do to not appear to be a major driver of the integrated assessment status in 2011-2016.

In addition, a number of substances that were assessed in the initial holistic assessment (HELCOM 2010), such as hexachlorocyclohexane (HCH, lindane) and dichlorodiphenyltrichloroethane (DDT) and its metabolites are no longer considered as of significant concern. Substances that appear to have decreased in concern, however, still warrant careful future checking and monitoring, to ensure that concentrations remain low and that alternative or secondary sources do not result in degraded environmental status. For example, hexachlorobenzene has recently been recorded at increasing levels in air at some European monitoring stations and concentrations in sediment have been found to increase in at Swedish offshore sampling stations (EMEP 2017, Apler and Josefsson 2016).

Figure 4.2.4. Trends in indicator substances or substance groups shown as counts of data series based on the type of assessment methodology applied.

Figure 4.2.4. Trends in indicator substances or substance groups shown as counts of data series based on the type of assessment methodology applied. The available data for which the trends are calculated differ between substances and stations, covering roughly the following years for each substance; polybrominated diphenyl ethers (PBDE): 1999–2016; mercury: 1979–2016; cadmium: 1985–2016; lead: 1979–2016; hexabromocyclododecane (HBCDD): 1999–2016; perfluorooctane sulphonate (PFOS): 2005–2016; benzo(a)pyrene: 1997–2016; anthracene: 1990–2016; non-dioxine-like polychlorinated biphenyls (PCB): 1978–2016; fluoranthene: 1997–2016, Cesium-137: 2011-2016, and for Tributyltin (TBT) and imposex: 1998–2016.

An overview of results for selected hazardous substances indicators is provided below. A more comprehensive overview is provided in the Thematic assessment (HELCOM 2018C).

Core indicators from the integrated assessment

Polybrominated diphenyl ethers (PBDEs) are toxic and persistent substances which bioaccumulate in the marine food web. The sum of six PBDE congeners are compared to the threshold value. The threshold value for biota is an environmental quality standard set to protect both the marine ecosystem, and humans consuming fish, from adverse effects. It is currently due for scientific re-assessment.

Polybrominated diphenyl ethers fail the threshold value for biota in all areas where they are monitored (Core indicator report: HELCOM 2018t, Figure 4.2.5). For sediments, the threshold value is achieved. For example the green area in the indicator summary map around the Åland Sea reflects an assessment based on the secondary threshold value in sediments, while there is a lack of data from biota in that area.

The use of polybrominated diphenyl ethers as flame retardant has been banned in most products in Europe since 2004. Therefore, decreasing concentrations are expected in the future. Out of the twenty-two stations where trends were assessed, downward trends were identified in five stations (both coastal and offshore). One station showed an upward trend.

In addition to polybrominated diphenyl ethers, several other man-made brominated substances have been found in the environment, but little is yet known on their effects on the environment and human health. To keep up with the developments and the emerging risks from such novel substances, it is important to continue and develop further collaborative monitoring and to map their occurrence and use in the Baltic Sea region (Kemikalieinspektionen 2017, Gustavsson et al. 2017).

Figure 4.2.5. Status assessment for polybrominated diphenyl ethers (PBDEs).

Figure 4.2.5. Status assessment for polybrominated diphenyl ethers (PBDEs). The summary map (main map) shows the status assessed by the one-out-all-out approach, meaning that the matrix-threshold combination with the worst status is shown for each assessment unit. Status based on the primary threshold in biota (top inset row) and secondary threshold in sediment (bottom inset row) is also shown. Status in biota is evaluated in herring, cod, flounder, dab, eelpout and perch. Red colour indicates that PBDEs fail the threshold value and green colour indicates that the measured PBDEs concentrations are below the threshold value (achieve the threshold). Symbols on map define data type and trend with downward triangles indicating decreasing concentrations, upward triangles indicating increasing concentrations and circles indicating no detectible trends. For more details, see HELCOM (2018t).

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Perfluorooctane sulphonate (PFOS) is considered a global environmental contaminant. It is a persistent, bioaccumulating and toxic compound with possible effects on the reproductive, developmental and immune systems in organisms, as well as on their lipid metabolism. The substance has been produced since the 1950s and was used in the production of fluoropolymers, and also to provide grease, oil and water resistance to materials such as textiles, carpets, paper and coatings. Perfluorooctane sulphonate has also been widely used in firefighting foams.

Concentrations of perfluorooctane sulphonate are below the threshold value in biota in all the monitored areas (Core indicator report: HELCOM 2018w). However, concentrations in seawater exceed the threshold value (EQS for water) where measured, which is reflected in the red area in summary map (Figure 4.2.6). There are a few downward trends in biota but no general trends are detected.

Perfluorooctane sulphonate has been banned in the EU since 2008 for most of its used categories, but it has been replaced with other similar substances (per- and polyfluoroalkyl substances; PFAS) which have widespread use. Most PFAS are highly persistent and bio-accumulating, and other PFAS (in addition to perfluorooctane sulphonate) are also a cause for concern. Some per- and polyfluoroalkyl substances (PFAS) are listed on the EU candidate list on ‘Substances of very high concern’ under the REACH regulation (ECHA 2017). Inclusion of additional PFAS as core indicators should be considered in the future to keep track of their use and occurrence in the Baltic Sea region.

Figure 4.2.6. Status assessment for perfluorooctane sulphonate (PFOS).

Figure 4.2.6. Status assessment for perfluorooctane sulphonate (PFOS). The one-out-all-out approach is used to summarise all matrix-threshold combinations (main map), with the primary threshold in biota (top inset row), secondary threshold in water (bottom inset row). Biota analyses is carried out in herring, cod, flounder, dab, eelpout and perch. Symbols on map define data type and trend with downward triangles indicating decreasing concentrations, upward triangles indicating increasing concentrations and circles indicating no detectable trends. For more details, see the Core indicator report: HELCOM 2018w).

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Three heavy metals were assessed: mercury, cadmium and lead. The heavy metals are toxic and some are bio-accumulated in marine organisms, causing harmful effects. The severity of effect mainly depends on the concentration in the tissues. Additionally, both cadmium and mercury are known to biomagnify, meaning that their concentration levels increase in organisms higher up in the food web. A major current source of heavy metals is the burning of fossil fuels, leading to atmospheric deposition.

Legislation is in place to decrease inputs of mercury, cadmium and lead to the Baltic Sea. The atmospheric deposition of cadmium and mercury to the Baltic Sea has decreased since the 1990s (Figure 4.2.7) All three metals are addressed in the Baltic Sea Action Plan, included in the European Water Framework Directive (Lead and cadmium in water, mercury in biota), and represented in the Marine Strategy Framework Directive.

Figure 4.2.7. Temporal trend in the total annual atmospheric deposition of cadmium and mercury to the Baltic Sea sub-basins.

Figure 4.2.7. Temporal trend in the total annual atmospheric deposition of cadmium and mercury to the Baltic Sea sub-basins. The right hand figures show values for the whole Baltic Sea. These are given as normalised atmospheric deposition to reflect the deposition independently of variability between years in weather conditions. Note that the scales between figures differ. Source: HELCOM (2017).

Mercury is analysed in fish muscle as a primary matrix. The most common species in which it is measured are herring and cod in the open sea area and flounder and perch in coastal areas. Mercury concentrations in fish muscle exceeded the threshold level in almost all monitored sub-basins indicating not good status (Core indicator report: HELCOM 2018x, Figure 4.2.8). The threshold value was also failed in some of the coastal areas. Good status was only achieved in the Arkona Basin and in a few coastal Danish and Swedish areas. There is no common general trend for mercury in fish muscle for the investigated time series, though eighteen downward trends, forty-three no detectable trends and five upward trends were recorded.

Figure 4.2.8. Status assessment for mercury.

Figure 4.2.8. Status assessment for mercury. The status is assessed in biota: herring, cod, flounder, dab, eelpout, perch and mussels samples. Symbols on the smaller inset map define data type and trend with downward triangles indicating decreasing concentrations, upward triangles indicating increasing concentrations and circles indicating no detectable trends. For more details, see the Core indicator report: HELCOM (2018x).

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For cadmium, data on concentrations in seawater, biota and sediment was used for the status assessment. Good status was not achieved in the Northern Baltic Proper, Western Gotland Basin, Eastern Gotland Basin, Gdansk Basin or Bornholm Basin, nor in some Polish, German and Danish coastal areas (Core indicator report: HELCOM 2018x, Figure 4.2.9). Only four downward trends were identified, with thirty-three not detectable trends and one upward trend recorded.

Figure 4.2.9. Status assessment for cadmium.

Figure 4.2.9. Status assessment for cadmium. The one-out-all-out approach is used to summarize all matrix-threshold combinations (main map), with the primary threshold in water (top inset row), secondary threshold in biota (middle inset row) and secondary threshold in sediment (bottom inset row) shown. Biota analyses is carried out on molluscs. Symbols on the map define data type and trend with downward triangles indicating decreasing concentrations, upward triangles indicating increasing concentrations and circles indicating no detectible trends. For more details, see HELCOM (2018x).

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Lead is most widely sampled in biota and sediment. It generally fails the threshold value in biota, with the exception of the Kattegat Bothnian Sea, and a few coastal areas. No general trend can be shown, although there were nineteen downward trends, forty-eight no detectable trends and three upward trends (Core indicator report: HELCOM 2018x, Figure 4.2.10).

Figure 4.2.10. Status assessment for lead.

Figure 4.2.10. Status assessment for lead. The one-out-all-out approach is used to summarize all matrix-threshold combinations (main map), with the primary threshold in water (top inset row), secondary threshold in biota (middle inset row) and secondary threshold in sediment (bottom inset row) shown. Biota analyses was carried out on herring, cod, flounder, dab, eelpout, perch and molluscs. Symbols on map define data type and trend with downward triangles indicating decreasing concentrations, upward triangles indicating increasing concentrations and circles indicating no detectible trends. For more details, see HELCOM (2018x).

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Cesium (Cs-137) is the greatest contributor of artificial radionuclides to the Baltic Sea. It emits ionizing radiation, which can have effects at the cellular level and lead to internal damage of organisms. The radionuclide was deposited in the Baltic Sea after the Chernobyl nuclear power plant accident in 1986. Since then it has bio-accumulated in marine flora and fauna, and has been deposited in marine sediments. The concentrations in herring have decreased from the high values in the 1990s in all sub-basins (Figure 4.2.11).

Figure 4.2.11. Temporal development of the mean concentration of cesium in herring

Figure 4.2.11. Temporal development of the mean concentration of cesium in herring (measured without head and entrails or in filets, by sub-basin). Concentrations are given as Becquerels per kilogram, calculated per wet weight. The green line shows the threshold value.

The concentrations of radionuclides are below the threshold value when measured in fish from the Arkona Basin, Bay of Mecklenburg and the Kattegat, indicating good status, but they are above the threshold value in all basins when measured in water (Core indicator report: HELCOM 2018y). Due to the steady half-life of radioactive decay it is expected that concentrations below the threshold value in biota and water may be achieved in all of the Baltic Sea by 2020.

Other indicators addressing hazardous substances

The main source of pharmaceuticals to the Baltic Sea come from humans and animals, via urine and faeces, as well as the inappropriate disposal of unused medical products into sewers. Municipal wastewater treatment plants are considered a major pathway for introduction to the aquatic environment, with an estimated release of about 1,800 tons of pharmaceuticals per year to the Baltic Sea. Current wastewater treatment processes are effective at removing only a few of the detected pharmaceuticals (UNESCO and HELCOM 2017). The fate and impacts of those pharmaceuticals in the environment is still largely unknown.

During 2003-2014, pharmaceuticals were detected in Baltic Sea water, sediment and biota, as well as in wastewater treatment plant influents, effluents and sludge. The most frequently detected pharmaceutical substances belong to the therapeutic groups of anti-inflammatory and analgesics, cardiovascular and central nervous system agents. Diclofenac – an anti-inflammatory drug -was detected in 25 % of samples for which it was analysed (UNESCO and HELCOM 2017).

An indicator for diclofenac is currently being tested in HELCOM (Figure 4.2.12). Pharmaceuticals represent a major group of substances of emerging concern and it is important that an understanding of their distribution, role and fate in the environment is developed.

Figure 4.2.12. Overview of sample location in Baltic Sea water (left and middle) and biota (right) where diclofenac concentrations have been assessed.

Figure 4.2.12. Overview of sample location in Baltic Sea water (left and middle) and biota (right) where diclofenac concentrations have been assessed. Samples in which diclofenac were detected are indicated by squares (left and right), with colours indicating good (green) and not good (red) status. Circles (middle and right) indicate samples in which diclofenac was not detected, with colours indicating the detection limit certainty, green having a detection limit below the set threshold value (i.e. reliable) and yellow having a detection limit above the set threshold value or unknown (i.e. uncertain reliability). The thresholds applied are provisional thresholds and the indicator is a pre-core indicator (HELCOM 2018aa).

White-tailed sea eagles are top predators in the coastal food web, which makes them highly vulnerable to hazardous substances that accumulate and biomagnify. The white-tailed sea eagle has suffered for decades from the effects of persistent chemicals in the Baltic Sea environment. Impacts have been apparent since the 1950s and it was identified at that time that widely used insecticides (DDTs) and possibly polychlorinated biphenyls were major causes. Bans on the use of these substances have been in place for decades and positive development has occurred since the 1980s.

Negative effects of long-standing environmental contaminants, as well as emerging new contaminants can become apparent in white-tailed sea eagles before they are visible in other species. Parameters describing the number of hatchlings in nests (brood size) and the proportion of nests producing young (breeding success) can inform on overall productivity (productivity), and can rapidly signal effects from contaminants. While changes in the abundance of adult birds might only occur over a period of several years, an increased mortality of eggs or chicks, and thus a lowered productivity, is often an early warning signal of elevated concentrations of hazardous substances.

The assessment shows that the white-tailed sea eagle productivity reached the threshold value in many coastal areas of the Baltic Sea (Core indicator report: HELCOM 2018ab). In German coastal areas productivity was calculated to be just below the threshold value due to low brood size. In the Gulf of Bothnia Finnish coastal areas, Gulf of Bothnia Swedish coastal areas and Latvian coastal areas brood size also narrowly failed the threshold value, and in the Åland sea Finnish coastal areas the breeding success parameter was at the threshold value (examples shown in Figure 4.2.13).

Figure 4.2.13. Mean annual productivity of the white tailed sea eagle.

Figure 4.2.13. Mean annual productivity of the white tailed sea eagle, estimated as the number of nestlings per occupied territory in coastal sub-populations of the Baltic Proper and Gulf of Bothnia (based on data from Sweden) from 1964-2014. The green line illustrates the threshold value of the core indicator. For more information, see the Core indicator report: HELCOM (2018ab).

Oil is the main fuel of ships in the Baltic Sea region, and large amounts of oil are transported across the Baltic Sea. Oil and other petroleum products are released into the sea intentionally or due to negligence, often as oil in bilge water or via dumping of waste oil. Oil may also be released during shipping accidents. Most oil spills are detected along the main shipping routes. Oil spills are a serious threat to the marine environment, causing toxic effects and death of marine animals. Even small amounts of oil on the sea surface can harm waterbirds by contaminating their plumage, which reduces their buoyancy and thermal insulation.

Illegal oil spills have been monitored using aerial surveillance since 1988 in the Baltic Sea area. The aerial surveys today are conducted by all HELCOM Contracting Parties with standardised methods, and cover nearly the whole Baltic Sea area. The effort is focused on the busiest shipping routes. The information collated through the aerial surveillance is used in the core indicator evaluation.

The core indicator ‘Operational oil-spills from ships” fails the threshold value in the Bothnian Bay, the Quark, Bothnian Sea, Åland Sea, Eastern Gotland Basin, Western Gotland Basin, the Great Belt, and the Kattegat during the assessment period 2011–2016 (Core indicator report: HELCOM 2018ac). The threshold values are set based on the volumes of oil spills into each sub-basin during a modern baseline status defined by the reference period 2008–2013, when the estimated volume of oil spills was at a historically low level. The long-term goal in HELCOM is to reach a level of zero oil spills.

Both the number of observed illegal oil spills and the estimated volume of detected oil have decreased in all sub-basins during recent decades (Figure 4.2.14). The size of single spills has also shown a decreasing trend, with a significant decrease in spills larger than 10 cubic meters. This decrease has been achieved despite no concomitant decrease in maritime traffic occurring, indicating that measures conducted to decrease oil spills to the environment have been successful.

Figure 4.2.14. The number of oil-spills detected in aerial surveillance by the Baltic Sea countries between 1988 and 2016.

Figure 4.2.14. The number of oil-spills detected in aerial surveillance by the Baltic Sea countries between 1988 and 2016. The number of flight hours are shown in the inserted figure. The size of the circles indicates the amount of spilled oil in cubic meters. The peaks in the amount of spilled oil detected in 1990 and 2004 were likely caused by single events. In 1990 an accidental spill due to a collision between the Soviet tanker Volgonef 1263 and the West German dry cargo ship Betty at the south coast of Sweden is the main cause, whereas the underlying cause for the high estimated amount of oil in 2004 is undocumented. The peak values highlight that single oil spills may introduce large amounts of oil to the environment, and underline the importance of estimating the volume of introduced oil when evaluating whether the pressure is at a level allowing the environment to reach good status. For more information, see the Core indicator report: HELCOM (2018ac).

Implications and future perspective

The assessment shows that hazardous substances remain a concern in the Baltic Sea, but also that policy and measures do have an impact. Long recovery times are often required for persistent historical contamination. Despite this, and the problem of re-release from historic sediment-deposited contaminants, initial signs of improvement can be detected.

Downward trends are seen for a number of the monitored substances or substance groups. For example, lead inputs have decreased markedly and shows among the largest number of declining trends. Furthermore, a number of substances, such as hexachlorocyclohexane (γ-HCH, lindane), and dichlorodiphenyltrichloroethane (DDT) and its metabolites (DDD, DDE) are no longer considered of significant concern in the Baltic Sea. The improved breeding success in the white-tailed sea eagle is attributed to such reductions. In future assessments it can be expected that radioactive substances will achieve their threshold value, and a number of other substances can be expected to show improvements. Also, it should be recalled that while strong initial decreases may often be observed, latter stages of improvement can be slow, as the levels get closer to the threshold values.

This positive development is however counteracted by the emergence of new contaminants of concern, and by the risk for re-emerging contaminants via secondary sources. Pharmaceuticals is one group of substances of emerging concern, with wastewater treatment plants being identified as a major pathway to the environment (UNESCO and HELCOM 2017). A number of pharmaceuticals considered to be of special concern to the aquatic environment have been included on a ‘watch list’ under the European Union directive regarding priority substances in the field of water policy (EC 2013b) in a drive to gain greater understanding on the fate and impact of these substances.