PCBs have generally been considered to be one of the global pollutants.

After the 70's, countries all over the world have taken steps to halt production and ban or limit the use of PCBs. The global accumulated amount of PCBs is estimated to be around 2 million tons. China started the production of PCBs in 1965 and ceased production at the end of 1974. Over the years, the accumulated amount has reached 10,000 tons. Of this amount, about 9,050 tons of chlorinated triphenyls have been used as soakers for transformers and about 1,000 tons of chlorinated pentaphenyls as additives in paints. When the PCBs ceased production, the 750,000 transformers containing PCBs were subsequently discarded as useless in the years 1980 to 1990.

Currently, most of them are being dumped and sealed in caves or in cellars. However, due to the long term storage, the rotting process and other damages, PCBs leakages occurred. The soil surrounding the dumping site has been found to have a higher content of PCBs.

Report on the areas polluted by the PCBs

A. Test results of the PCBs content in the highly contaminated areas around the dumping sites of the disused transformers.

1. Soil samples taken around the said areas were found to contain 788 mg/kg (dry weight) of PCBs. Compared to the documentary report, the soil in Tibet is not directly affected by PCBs was found to contain only 0.625 - 3.501 ug/kg (dry wt) of PCBs.
   
2. Samples of the subsoil taken from the rivers around the contaminated areas were found to contain 691 ug/kg (dry wt) of PCBs. Compared to the national documentary report, subsoil picked up from the Songhua River was found to contain 25.4 - 70.3 ug/kg (dry wt) of PCBs.
   
   

   The concentrations of PCBs in soiland sediment of various environment

   
   
3. We collected two samples of the subsoil from the river, one at the depth of sample A, 0.5 meter and the other one, sample B at 1 meter.
   
   

   The PCBs contents of sediment, the depth of 0.5 and 1 meter from the river

   
   Their PCBs content was tested. It was found the sample A contained 430 ug/kg (dry wt) of PCBs and sample B contained 17.5 - 25.8 ug/kg (dry wt.).
   
   This shows that as the depth of the subsoil increases, the PCBs content decreases substantially. The findings give rise to two other interpretations. Firstly, the water solubility of PCBs is quite low, and secondly, the mobility of the PCBs in the subsoil is limited.
   
4. Determination of the PCBs content in the fish muscle samples collected from different areas.
   
   

   The concentrations of PCBs in fish tissues (µg/kg)

   Sample 1:
   Muscle of carps caught in existing highly contaminated river: the PCBs content was 691 ug/kg

   Sample 2:
   Muscle of carps caught in the river which had been contaminated by PCBs two years ago and since then unpolluted: the PCBs content was 22.6 ug/kg

   Sample 3:
   Muscle of Silver Pomfret (Euphrasen) and that of Dragonhead Fish (Buchaman Hamilton) caught in uncontaminated waters: their PCBs content was 0.38 ug/kg and 1.38 ug/kg respectively.
   It is obvious, therefore, that:
   
   (a) fish caught in the contaminated waters has higher PCBs content than that in the uncontaminated waters, and
   (b) fish caught in existing contaminated waters had PCBs content a few hundred or even a thousand times higher that that in the uncontaminated water.
   

5. Determination of the total amount of PCBs and other PCB-related substances in the contaminated water and that of the fish caught in it.

   Percentage composition of PCB congeners in fish and water

   Studies showed that the water sample contained PCBs weighing 2.97 ug/kg. That means the fish muscle sample is more than 7,000 times higher that that of the water sample. From the investi8gation done on the distribution of the other PCB-elated substances, we noticed that in the water sample, the PCBs content with 2.3 chlorine substitution was relatively higher, but in the fish muscle sample, with 6.7 chlorine substitution, the PCBs content was relatively higher. The reasons are: (1) PCBs with low chlorine substitution has higher water solubility, but PCBs with high chlorine substitution has relatively higher fat solubility; and (2) PCBs with low chlorine substitution can easily be metabolized and excreted by aquatic living things but the bioaccumulation of the PCBs with high chlorine substitution in the bodies of the aquatic living things is more stable.

   From the analysis of the fish muscle samples, we discovered five types of PCB-related substances with higher toxic level but in the water sample, there was only ONE. The PCB content in the fish muscle sample was 2.31 ug/kg but that in the water sample was 0.06 ug/kg. Hence, we can infer that aquatic living things have a high rate of bioaccumulation in their bodies not only for PCBs but also for highly toxic PCB-related substances.
   
6. Determination of PCB content in the muscle, liver, bile and egg of the female carp caught in the contaminated river.
   
   

   Concentration of PCBs in various fish organs

(A) The results indicated that the PCB content in the fish body followed a distribution trend of liver > egg > bile > muscle. The PCB content of the fish's liver was 8 times that of the muscle.

(B) Results of the second investigation into the PCB content conducted in the Songhua River.

Preliminary investigation into the drainage system along the river revealed no direct source of PCB pollution.

Concentration of PCBs in water, sediments and fish of second Songhua River with no direct source of PCB pollution

Investigation Results:

1. Rate of PCBs contamination of the river water was 31.5% and the average concentration rate was 0.013 ppb.
   
2. Rate of PCBs contamination of the subsoil was 100% and the concentration rate was 0.12-1.04 ppb, the average value being 0.62 ppb.
   
3. Rate of PCB contamination of the fish body was 100%, the concentration rate was 6.4-214 ppb.
   
   This showed that the concentration rate in the river water was not high but that in the fish body was much higher, the bioaccumulation rate was more than 10,000 times.
   
4. Investigations done on the different body parts of the fish revealed that the PCB content in the liver, brain and other high-fat organs was significantly higher.

(C) The condition of pollution in the well-preserved primitive environment of Tibet's South Kabawa hilly regions.

The concentrations of PCBs in Tibet's South Kabawa hilly regions (ppb)

Investigations showed little PCB content in the river water and ice water. The PCB content in the ice water was 0.0105 ppb and that of the river water was 0.008 ppb, meaning ice water PCB content was slightly higher than that of the river water. The date, when compared to that of the documentary report on the South Pole's ice water, lake water and sea water, showed higher level of PCB contamination.

The different types of soil of the grassy marshland, from 2,600 meters to 4,000 meters above sea level were found to have different degrees of PCB pollution, their PCB content ranging from 0.113-5.934 ppb.

The above information clearly indicates that PCB pollution has extensively affected our environment and it is time for all of us to take this matter seriously.

Lately, our government has taken further steps to solve the problems of PCBs pollution. They are:

1. To include PCBs in the list of "National Hazardous Substances" and to introduce new regulations for their control.
   

   a.	All PCBs-related wastes are subjected to special treatment.
   b.	Factories have to apply to the relevant authorities for approval for the use of PCBs.
   c.	To ban the transit of PCBs wastes through Chinese territory.

2. To set permitted value for PCBs content in waste materials at 50mg/kg.
   
3. To dispose of waste materials with PCBs content of 50-500mg/kg at designated dump sites or landfills. Those with PCBs content above 500mg/kg must be disposed of by using high temperature combustion technology. PCBs wastes that are not suitably treated must be collectively and safely stored or sealed at designated sites according to the instructions of the relevant authorities.
   
4. To formulate regulations to control the import of used products containing PCBs. Those with PCBs content higher than the permitted value will not be allowed entry into country.

We believe from now on, more and more laws and regulation will be enacted and stricter enforcement measures will be taken to curb the menace of PCBs pollution in China.