The use of cadmium stabilizers is exclusively connected to the manufacture of PVC. Many PVC- applications were stabilized with cadmium in the beginning of the 1970's. The number of applications and the production quantities have decreased since 1980, due to the increasing environmental concern with respect to cadmium. The only large application in which cadmium stabilizers are still used, are outdoor PVC window profiles. These profiles had a market share of 75 % of the use of aU cadmium stabilizers in 1989 in the FRG. Minor uses are roofing and swimming pool foil and other outdoor PVC profiles [go]. Substitutes for these applications are available, but due to the long-life guarantees which are common in the building industry, long- lasting tests with the substitutes must yield positive results, before substitution takes place [78,80].
Although PVC-stabilizers are now also used in master-batches, in order to reduce occupational health hazards and emissions in the PVC processing plants [82], this has not always been the case. For 1988 the master-batch procedure is assumed to be applied for all products which are being made in the basin.
Aqueous cadmium emissions were, using the old procedure, caused when wet scrubbers were used to clean (cadmium stabilizer) dust-laden gas. In case liquid stabilizers were used, minor amounts of the stabilizers might have ended up in the sewer.
In the basin 8 companies are manufacturing PVC. One plant is located in Sins in Switzerland, six are located in Germany (Marl, Koeln, Frankfurt am Main, Rheinberg, Ludwigshafen and Waldshut) and one plant is located in Rotterdam in The Netherlands.
If it is assumed that
(i) cadmium stabilizers are used in all plants and
(ii) the magnitude of the stabilizer use is proportional to the magnitude of the PVC production capacity,
then the stabilizer use can be divided over the individual locations. For 1985 this leads for the FRG (in which additionally three production sites are located outside the basin) to the figures given in table 4.8.
Table 4.8 The relative production capacities and the cadmium stabilizer use for 1985 for two different scenario's
the total PVC production capacity in the FRG in 1985 is 1445 ton [29].
the total domestic cadmium stabilizer use is 494 ton [29].
I assumption that all PVC processing plants use cadmium stabilizers is probably incorrect. A PVC window profile is only one out of many PVC products. Companies specialize on certain products rather than cover an entire product's application market. The second point to make is that it is not sure that all plants indeed need stabilizers. If the manufacturing process stops at the point where the PVC resin has been formed, the use of PVC stabilizers is not always required.
Additional information for this inventory is offered by the Deutsche Kommission zur Reinhaltung des Rheins [62] which lists by 1985 three in-basin PVC manufacturing plants as major industrial cadmium dischargers. These companies are located in Rheinberg, Ludwigshafen and Marl. The following data are available.
Plant Annual emission (kg Cd) concentrating on PVC, whereas the locations Rheinberg and Ludwigshafen have many other activities as well. Therefore the emission factor should be based on the plant in Marl.
Given the fact that only three out of six in-basin plants are mentioned as cadmium dischargers it is not convincing to suppose that all in-basin PVC plants actually used Cd- stabilizers in their PVC processing. An extra difficulty in this respect is the fact that PVC plants outside the basin have not been discussed by the Deutsche Kommission zur Reinhaltung des Rheins [62].
Two possibilities are discussed in this study:
-1- all companies inside the FRG did use Cd-stabilizers and the use was proportional to the PVC production capacity;
-2- only three companies, Rheinberg, Ludwigshafen and Marl, used Cd-stabilizers and their use was proportional to their PVC production capacity.
The figures corresponding with the second possibility are also given in table 4.8. Possibility -1- leads to the high extreme for the emission factor related to the PVC manufacturing plant in Marl, whereas possibility -2- leads to a lower value. The specific emission factor for 1985 is calculated as follows:
Possibility -1-
-
the cadmium stabilizer use was 140 ton Cd;the emission (as given by ref. [62]) was 225 kg Cd;
the 1985 emission factor estimate then is 1.6 kg Cd/ton Cd processed or 0.5 g Cd/ton PVC processed.
Possibility -2-
the cadmium stabilizer use was 281 ton Cd;
the emission was 225 kg;
the 1985 emission factor estimate then is 0.8 kg Cd/ton Cd processed or 0.25 g Cd/ton PVC processed.
Based on these calculations the 1985 emission factor for the aqueous cadmium emission during PVC manufacturing is given as: 0.8
-
1.6 kg Cd/ton Cd processed.The other two plants (Rheinberg and Ludwigshafen) would provide a higher emission factor. In case of Rheinberg this is due to potash production which is an additional minor source of aqueous cadmium emission. For the Ludwigshafen plant no explanation for the discrepancy is available. However, there's no evidence that the cadmium use of these plants is proportional to the production capacity. That assumption might also cause the discrepancy with the real data.
Backcasting the emission factor provided here, to the 1970's is even more tricky, due to lack of data. For two reasons, no spectacular decrease of the emission factor is assumed since the 1970's.
-1- Until the 1980's the magnitude of the emission was such that it was not considered as significant;
-2- as a consequence the cadmium emission due to PVC manufacturing has never been addressed, so there have been no incentives to improve the situation, apart from the tariffs in the German waste water legislation, which per unit emitted cadmium have increased significantly in the 1980's [83] l .
Based on these two remarks the following estimated emission factors are given, based on an expected trend, without any supporting data:
Period Cd-stabs-use Factor Emission (FRG)
(ton Cd/yr) (kg Cd/ton Cd) (ton Cd/yr)
For Switzerland the emission has been negligible 2. For The Netherlands, using these emission factors, Dutch statistics on cadmium stabilizer use and the assumption that cadmium stabilizers are used, the emissions in Rotterdam have been negligible as well
'.
1 The German Waste Water Discharge Act of 13 September 1979 determines that per unit aqueous discharge a fee has to be paid. For cadmium discharges the unit is 100 g/yr.
When the emission lies below 100 units/yr (or 10 kg/yr) the discharge is free of charge.
The fee per unit is given here as a function of time.
2 The Swiss in-basin production capacity for PVC was 30,000 tons in 1985, which in case cadmium stabilizers had been used would have created an emission of the order of magnitude of ten to twenty kilograms cadmium per annum.
3 The Dutch in-basin production capacity for PVC was around 200,000 tons, which might have caused, if cadmium stabilizers had been used, an emission of about 100 kilograms.
However, the plant is located next to two large wet phosphoric acid production plants which until 1988 together emitted at least 10 tons of cadmium per annum.