Riverine inputs of heavy metals

	Authors: HELCOM PLC - Group Editor: Seppo Knuuttila, Finnish Environment Institute

Key message

In 2003 the reported riverine (including coastal areas) mercury load entering the Baltic Sea amounted to 7.3 tonnes, the lead load to 285.8 tonnes, and Cd load to 8.1 tonnes. During the period 1994-2003 riverine heavy metal loads (notably Cd and Pb) seems to have decreased for most of Contracting Parties. However, incomplete data from some countries makes it difficult to draw conclusions concerning the total heavy metal load into the Baltic Sea.

Results and assessment

Relevance of the indicator for describing developments in the environment

High concentrations of heavy metals in biota of the Baltic Sea is mainly caused by loading from land-based sources. About 50 % of mercury, 60-70 % of  lead, and 75-85 % of cadmium enters the Baltic Sea as waterborne (i.e. via rivers or as direct discharges). Another significant contributor to the total heavy metal load is atmospheric deposition.

Policy relevance and policy references

Excessive heavy metal concentrations may pose a health risk to the marine biota and human. In the Baltic Sea high concentrations of mercury, cadmium and lead have been measured e.g. in fish, in the eggs of waterfowl, and in the seal tissues. In the Baltic Sea measured concentrations of heavy metals have been even an order of magnitude higher than concentrations in the North Sea. The main reason behind the high concentrations in the Baltic Sea is intense industrial activity, high amount of population, and above all long renewal time of water. Quantified annual information on waterborne inputs of heavy metals is needed for evaluation of long-term changes of  heavy metal concentrations in biota and the state of marine environment.

Assessment

Due to the incomplete data on heavy metals, a good quantitative picture of the loads entering the Baltic Sea could not be given. Shortcomings in national monitoring programs and the lack of proper laboratory equipment in some countries meant that heavy metal figures were not obtained in many cases, or the loads reported are not fully reliable (no harmonized detection limits in all HELCOM countries). Also different calculation methods have been used in the countries if the measured concentrations have been below the detection limit. The data sets of unmonitored rivers and coastal areas are even more incomplete.

A few big rivers account for the major part of the total riverine heavy metal loads. Comparing the riverine inputs to the different sub-basins, the Gulf of Finland received the highest lead load, while mercury inputs were highest for the Baltic Proper (Polish rivers accounted for 90 % of the total mercury load). For cadmium such estimates cannot be given, because of the missing data.

The riverine heavy metal loads also vary to some extent with runoff from year to year, but not to the extent as nutrient loads due to their origin (industry, waste water treatment plants). To be able to evaluate the reductions of heavy metal load from land-based sources comparable, reliable and extensive long-term data (since early '80s) should be available.

References

Click image to enlarge! 

Figure 1. Riverine load of Lead to the Baltic Sea in 2003 for the 9 riparian countries. Units: tonnes.

Figure 2. Riverine load of Cadmium to the Baltic Sea for the 9 riparian countries. Units: tonnes.

Click image to enlarge!

Figure 3. Riverine load of Mercury to the Baltic Sea for the 9 riparian countries. Units: tonnes.

Time series of riverine inputs to the Baltic Sea for Lead, Cadmium and Mercury including the river and coastal flow in 1994-2003.

Figure 4. Time series for riverine load of Lead in t/year to the Baltic Sea and the river and coastal flow in m³/s for the period of 1994-2003 of the 9 riparian countries. (Note variable scales in the graphs). CLICK IMAGE TO ENLARGE.

Figure 5. Time series for riverine load of Cadmium in t/year to the Baltic Sea and the river and coastal flow in m³/s for the period of 1994-2003 of the 9 riparian countries. (Note variable scales in the graphs). CLICK IMAGE TO ENLARGE.

Figure 6. Time series for riverine load of Mercury in t/year to the Baltic Sea and the river and coastal flow in m³/s for the period of 1994-2002 of the 9 riparian countries. (Note variable scales in the graphs). CLICK IMAGE TO ENLARGE.

Table 1. Riverine and coastal inputs of Lead of 9 countries in 1994-2003 as totals, t/year.

 *Reported upper values have been used

Table 2. Riverine and coastal inputs of Cadmium of 9 countries in 1994-2003 as totals, t/year.

 *Reported upper values have been used

Table 3. Riverine and coastal inputs of Mercury of 9 countries in 1994-2003 as totals, t/year.

 *Reported upper values have been used

Meta data

Technical Information

1. Data source:

Data have been collected by the Contracting Parties of HELCOM and submitted to the Pollution Load Compilation database (PLC database). The data base is located in Finnish Environment Institute (SYKE).

2. Description of data: 

The data are based on annual average concentrations of heavy metals (Cd,Pb and Hq) and mean flows (m³/s). The Contracting Parties have calculated the annual loads (t/a) of monitored and unmonitored rivers and coastal areas. Monitored river loads are based on measurements, unmonitored river loads and coastal area loads on estimates, respectively.

3. Geographical coverage:

Drainage area of the Baltic Sea, 9 countries; Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia and Sweden, including the drainage area of the Baltic Sea in Belarus, Czech Republic, Norway, Slovakia and Ukraine. 

4. Transboundary rivers:

To avoid double data reporting of the transboundary rivers, their loads have been included in as follows:

River Tornio (Finland)/Torne älv (Sweden): in the Swedish data

River Narva (Russia and Estonia): in the Estonian data

River Oder (Poland): in the Polish data

5. Temporal coverage:

Harmful substance load in 1994-2003

6. Methodology and frequency:

Variable, basically as agreed on the PLC-4 guidelines 

Quality information

1. Strength and weakness:

A full quantitative picture of the heavy metal loads entering the Baltic Sea could not be given, because of incomplete data, shortcomings in national monitoring programs, and the lack of proper laboratory equipment as well as different calculation methods.

2. Reliability, accuracy, robustness, uncertainty:

Heterogeneous data in space and time and may cause some variation between years. Due to robust analysing methods in some countries reported loads might be too high.

Missing data

1.  Monitored rivers

Denmark: Heavy metals

Latvia: All data of 2003, Hg

Lithuania: Hg

Russia: all nitrogen fractions in 1994-1999 and all data of 2003

2.  Unmonitored rivers and coastal areas

Latvia: All data of 2003

Russia: all nitrogen fractions and part of the phosphorus data

Denmark: heavy metals

Missing data have been listed in table 4.

Table 4. Missing data on monitored rivers, unmonitored and coastal areas in 1994-2003 by parameter.

(DE = Gemany, DK = Denmark, EE = Estonia, FI = Finland, LT = Lithuania, LV = Latvia, PL = Poland, RU = Russia, SE = Sweden, years indicated after abbreviation)