Contaminants and nutrients in seabed sediments

Historical and present pollution of the Baltic Sea from contaminants and eutrophication from nutrients has led to some contamination of the underlying sediments. The Baltic Sea receives contaminants from several different sources including atmospheric, fluvial and point sources, although the situation is improving and much of the pollution is due to historic industrial discharges. Background concentrations of inorganic compounds (metals) depend on natural input (e.g. derived from the mineral composition of the geology), with further contributions from anthropogenic sources /45/. By contrast, the origin of organic contaminants is mainly

anthropogenic. The distribution patterns of contaminants in the Baltic Sea are complex, as they are often incorporated into particles on the seabed or adsorbed onto the suspended particles in the water. The majority of contaminants are associated with fine-grained sediments (e.g. silts and clays), due to their large surface area and the negative electrical charge of their surface, and particulate organic matter (POM).

Sediment samples from the NSP2 route were analysed for concentration of metals, organic contaminants and nutrients. The results of these surveys are summarised in Appendix 4. It should be noted that direct comparison of sediment data between countries is not possible because of differences in sampling methodology, analytical techniques and whether samples have been normalized to account for sediment properties.

In general, the results showed that seabed sediment concentrations of both metals and organic contaminants were highest in the Gulf of Finland and in the southern Baltic Proper. These areas coincide with sheltered and/or deep areas that are zones of sedimentation for fine-grained sediments and POM (see Section 9.2.1.3), as well as areas which are influenced by freshwater run-off (which may be impacted by industrialisation in the catchment area). For the most part, contaminant levels in the sediments only showed slight exceedances when compared against guidelines such as the

Oslo-Paris Convention, Convention for the Protection of the Marine Environment of the North-East Atlantic (

OSPAR) /46/, /47/ and HELCOM /48/, /49/.

The average concentrations of nitrogen and phosphorous in surface sediments along the proposed NSP2 route indicate a relatively uniform distribution, with a tendency for higher concentrations in areas of fine-grained sediment.

The following sections briefly describe the sediment contaminants recorded in each of the NSP2 baseline surveys with particular attention to given to where these concentrations exceeded guideline values. Appendix 4 sets out the contaminant concentrations (minimum and maximum values) recorded in the baseline surveys.

Sediments in Russian waters

The survey in Russian waters was conducted in August 2016 at four stations along the proposed NSP2 route. Five sampling points were selected within each station. Analysis was performed for three layers within each sample: 0-2 cm, 2-10 cm, 10-30 cm. In the nearshore area, samples were taken from 11 locations along the proposed NSP2 route.

The concentrations of metals and organic contaminants in the samples were compared against the St. Petersburg regional norms for bottom sediments in the water bodies /50/. For the components not included in the regional norms, the Finnish guidelines for dredging and deposition of dredged materials /51/ have been used as the methodology for values normalisation, and the approach for sediment quality assessment is comparable.

On average, the results indicated that sediments in deeper waters (>60 m) had higher levels of contamination in all measured parameters. There was a strong correlation observed between the finer sediments found in deeper waters, which have a higher silt/clay fraction. These deeper areas represent zones of sedimentation where contaminants have accumulated over time.

Samples taken from the nearshore sector showed no or only slightly contaminated concentrations.

Exceedances for metals were observed as follows (/51/):

• Concentration of copper exceeded the regional norm at nine sampling points within three stations (mostly at depths ranging between 65-70 m and for one sampling point at 36 m), with a maximum concentration of 1.36 times the regional norm;

• Concentration of lead exceeded the regional norm at one sampling station (68 m water depth), with a concentration 1.46 times the regional norm;

• Concentration of zinc exceeded the regional norm at two deep water sampling points (66 m and 70 m water depth), with a maximum concentration 1.13 times the regional norm.

Vertical distribution of heavy metals was relatively constant in all analysed depths (0-30 cm) and at the same level as other samples collected from the Gulf of Finland in the Finnish EEZ.

Concentrations of organotin compounds (

tributyltin,

TBT) were typically below the limit of detection. At the few stations where organotin compounds were detected, monobutyltin was the main constituent. No exceedances were observed when compared with Level IB (concentration level for the assessment of the eligibility for dumping of dredged material) and higher values in the Finnish guidelines /51/, as Russian norms do not have guideline values for these compounds.

Dioxin and furan levels were slightly higher in the deeper stations, with no clear difference between surface and deeper sub-samples.

Polycyclic aromatic hydrocarbon

(PAH) and

polychlorinated biphenyl

(PCB) levels were consistent across all stations both in spatial and vertical directions. No exceedances of the regional norms were detected.

In Russian waters, concentration of nitrogen reached 1%, phosphorus (5,440 mg/kg) in surface sediments, with a tendency for higher concentrations in samples taken from deep water stations.

Sediments in Finnish waters

The survey in Finnish waters was conducted in December 2015 and included seven stations along the NSP2 route. Eight samples were collected from each station. The concentrations of metals and organic contaminants in the samples were compared against the guidelines for dredging and depositing dredged materials by the Finnish Ministry of the Environment /50/.

Based on all data, no major differences were detected in the level of contamination between stations, although the results show that concentrations of metals were highest in the western part of the route, where sediment properties are favourable to attachment by chemical compounds. Notwithstanding this, all metal concentrations were within the range of the lowest guideline value (1, 1A and 1B⁵). An exception was cadmium, which showed a slight exceedance of the lowest guideline value at three stations. In single samples, nickel and copper exceeded the higher guideline value 2⁶ at three stations (four samples) and one station (one sample) respectively.

The normalised median concentrations of dioxins and furans were within the range of guideline values 1A and 1B⁷ at all stations. The highest single concentrations that exceeded guideline value 2 were observed in three samples. Two of these samples were taken from the easternmost part of the proposed NSP2 route in Finland, near the Russian border (likely due to historic pollution from the River Kymijoki).

PCB concentrations of three congeners exceeded guideline value 2 at one station (one sample taken from the surface sediment at 0-2 cm depth) in the survey area closest to Koverhar. The remainder of samples were below the limit of detection, suggesting only localised contamination.

PAHs were observed sporadically in eastern stations and more consistently in western stations within Finnish waters, with the exceedances of the lowest guideline values. Organotin

5 1: concentration level represents naturally occurring background level. 1A: no harm is expected to be caused to aquatic organisms, even during long-term exposure; concentration level is below the PNEC level. 1B: no harm is expected to be caused to aquatic organisms during short-term exposure.

6

7 HELCOM and OSPAR have developed environmental assessment concentration (EAC) values for organic compounds.

compounds, mainly TBT, were present at all stations. TBT concentrations were highly variable between stations, but all were within the range of one of the lowest guideline levels, 1A.

Sediments in Swedish waters

The survey in Swedish waters was conducted in October 2015 and included 51 sampling stations for sediment analysis. One sample was collected from each station. The concentrations of metals and organic contaminants in the samples were compared against the Swedish Environmental Protection Agency (EPA) classification for the assessment of environmental quality /52/ , Swedish Agency for Marine and Water Management (SwAM) thresholds (cadmium and lead) /53/ and HELCOM thresholds.

In general, the results showed that concentrations of heavy metals and organic contaminants were higher at greater depths, in zones of sedimentation in the eastern Gotland Basin (from east of Hoburgs Bank to the Swedish/Finnish border). According to the Swedish EPA classification, the average concentrations of metals along the proposed NSP2 route in Swedish waters were generally within class 1, meaning “no deviation from natural background concentrations”.

However, the following exceedances were observed:

• Average concentrations of cadmium along the northern part of the route (comprising 17 stations) were classified as class 2, meaning there was a “small deviation from background concentrations”;

• Average concentrations of mercury along the central part of the route (comprising 17 stations) were classified as class 3, meaning there was a “deviation from background concentrations”.

In addition, samples from four stations in the middle part of the route exceeded the HELCOM effect low range (ERL) value for mercury, indicating “bad status”.

In terms of organic contaminants, the survey measured the concentrations of PAHs and PCBs, which have a high potential to accumulate on organic material in sediments and are resistant to degradation. Of the 10 PAH compounds measured, seven were below the EAC values at all stations. Two PAH compounds (indenol(1,2,3-cd)pyrene and benzo(g,h,i)perylene) exceeded the EAC values in several samples taken from stations along the northern and central parts of the route in Swedish waters and are considered to be present in “high levels” according to the Swedish EPA classification.

The levels of PCBs were below detection limits at the majority of stations along the proposed route. At the few stations where PCBs were detected, there were no exceedances of EAC values.

The levels of organochlorine pesticides (chlordane,

hexachlorocyclohexane

(HCH) isomers,

dichlorodiphenyltrichloroethane

(DDT) (and its degradation products

dichlorodiphenyl-dichloroethylene

(DDE) and

dichlorodiphenyldichloroethane

(DDD)) and

hexachlorobenzene

(HCB)) in sediments were generally below EAC values with the exception of two stations, which showed exceedances in the concentration of DDD.

The average concentrations of nitrogen and phosphorous in surface sediments indicate a relatively uniform distribution along the proposed NSP2 route in Swedish waters, with a tendency for higher concentrations in areas of fine grained sediment, particularly of nitrogen /32/. The concentration of total nitrogen also correlated closely with organic carbon in sediment. There was little variation in nutrient concentrations with sediment depth and no consistent trends were observed.

Sediments in Danish waters

The survey in Danish waters was conducted in October 2015 and included 14 stations along the proposed NSP2 route for sediment analysis. One sample was collected from each station. The

concentrations of metals and organic contaminants in the samples were compared primarily against the background assessment criterion (BAC), ERL and the EAC developed by OSPAR⁸ /46/, /47/.

In general, higher concentrations of metals were found in sediments taken from the deeper water stations located in the Bornholm Basin (and northern part of the route within Danish waters), where sediments are rich in organic content and have a high silt/clay fraction. The following exceedances were observed:

• Concentrations of lead, copper and nickel exceeded the BAC and/or ERL at nine stations in the northern and central part of the route;

• Concentrations of cadmium exceeded the BAC at one station in the northern part of the route;

• Concentrations of zinc exceeded the BAC at eight stations in the northern and central part of the route;

• Concentrations of mercury exceeded the BAC at four stations in the northern part of the route.

There were no exceedances of either the BAC or ERL of arsenic or chromium. No BAC or ERL is given for cobalt and vanadium.

The concentrations of PAHs were also highest in deeper water sediments that are rich in clay and where bottom waters have little to no oxygen. Exceedances of ERL were observed for three of the PAHs analysed, namely indeno-(1,2,3-cd)pyrene (at six stations), dibenz(a,h)-anthracene (at two stations) and benzo(ghi)-perylene (at six stations) along the northern and central part of the route.

All measurements of PCBs were below the EAC values, and in 6 of the 14 samples, all PCBs were below the detection limit.

The levels of organochlorine pesticides (chlordane, HCH, DDT (and its degradation products DDE and DDD) and HCB) in sediments were generally below ERL values with the exception of four stations in the northern and central part of the route, which showed exceedances in the concentration of DDE. Organotin compounds (TBT or its degradation products) were detected at most stations. However, an exceedance of the EAC threshold was only observed for TBT at six stations in the northern and central part of the route.

Concentrations of nitrogen did not show a correlation with water depth, with highest average concentrations recorded at both the deeper and shallower water stations. The lowest concentrations were recorded in those stations closest to Bornholm. Conversely, concentrations of phosphorous did show a correlation with water depth, with the highest average concentrations recorded at deeper water stations and the lowest average concentrations recorded in the shallower stations.

Given the proximity of the proposed NSP2 route to the chemical munitions dumping site, sampling in Denmark also considered concentrations of CWAs. The results are summarised in Section 9.14.2 and indicate that the highest concentrations of CWAs and their degradation products were found at stations along the middle and northern parts of the route, to the east and north-east of Bornholm.

8 The BAC is considered to represent background concentrations without anthropogenic influence, the ERL represents a limit above which negative effects may be expected, and the EAC represents the contaminant concentration in sediment and biota below which no chronic effects are expected to occur in marine species, including the most sensitive species.

Sediments in German waters

The survey in German waters was conducted in winter 2015/spring 2016 and included 42 sample stations located within the sheltered Greifswalder Bodden and another 63 stations in the exposed Pomeranian Bay. The concentrations of metals and organic contaminants in the samples were compared against guideline values set by the Joint Transitional Arrangements for the Handling of Dredged Material in German Federal Coastal Waterways (GÜBAK) and waste law provisions (LAGA-TR20).

In general, higher concentrations of metals were found in sediments with high silt content, and levels of contamination were lowest in the Boddenrandschwelle shoal, an area between Greifswalder Bodden and Pomeranian Bay. However, concentrations were generally low, because the silt content of sediments along route is generally low as well. No exceedances of guideline values were detected.

Concentrations of organic pollutants (including PAH, PCBs, organochlorine pesticides and TBT) were generally low in both areas, mainly below detection limit, and no exceedances of guideline values were observed.

In general, nutrient concentrations also appeared to be low and showed a correlation with sediment properties such as grain size and TOC. Again, no exceedances of guideline values were detected. Average concentrations were highest in areas of fine-grained material such as Greifswalder Bodden /54/ .

Hydrography and seawater quality

In document Nord Stream 2 April 2017 (Sider 170-175)