Critical review of the Dutch calculations

Many of the estimated metal fluxes, metal risk ratios and other quantitative data presented in the book, "Heavy Metals: A Problem Solved?", edited by Ester van der Voet, Jeroen B. Guinée and Helias A. Udo de Haes (2000) are quite surprising, to say the least. Since the book, published by Kluwer Academic Publishers may have a strong impact on the philosophy and on the decisions to be taken by environmental authorities and politicians in many European countries, it is necessary to take the data presented seriously and subject them to a careful scrutiny, in order to assess the credibility of both the numerical results of the modelling and the general conclusions reached by the authors.

In section III.1 of the book, the authors conclude that "in most cases emissions constitute only a small part of the total fate of the metals. This does not imply that these emissions cause no problems: metals are toxic even in small doses." However, the quantitative data on emissions of metals in the Netherlands presented in Figure III.1.3 in the book clearly indicate that the emissions would be extremely high; in fact, if the data were correct, there is no question that a very serious metal contamination of the Dutch environment is existing. The data given in Table 3.7 can be extracted from Figure III.1.3 in the Dutch book.

Table 3.7. Total emissions of metals to the Dutch environment in 1990 and at a steady-state scenario, as well as the main receiving compartment, according to data in van der Voet, Guinée and de Haes, 2000.


Total emission in 1990

Tot. emis. at steady state

Main receiving compartm.


1,250 ktonnes

2,500 ktonnes

Agr. soils (1,900 ktonnes)


5,300 ktonnes

11,900 ktonnes

Non-agr. soils (7,500 kt)


1,150 ktonnes

1,400 ktonnes

Agr. + non-agr. soils


15 tonnes

22 tonnes

Agr. soils (10 tonnes)

Just for comparison with the metal emissions in another European country with approximately the same population, Sweden, it can be mentioned that the total emissions of copper to the Swedish environment in the mid-1990s were estimated to a little more than 200 tonnes, of which somewhat more than 100 tonnes were emitted to the aquatic environment (L

& L - Cu). In addition to the 200 tonnes to the natural environment, some 150 tonnes were introduced to agricultural soils. Thus, the total of about 350 tonnes of copper "emitted" in Sweden constitute less than 0.03% of the reported emissions in the Netherlands.

A similar comparison for zinc, based on data from (L & L - Zn), results in a fraction of about 0.06% as the Swedish emissions related to the Dutch emissions. Only the figures for cadmium seem to be in a reasonable order of magnitude.

The authors explain the great differences between the 1990 data and the steady-state data in the following way:

"The increase of steady-state emissions to agricultural soils compared to 1990 emissions is significant for all metals and is due to increasing flows of organic manure and of source-separated vegetable, fruit and garden waste (. . .). The ultimate source behind these increasing flows of copper and zinc is animal fodder."

In their evaluation of the present metal management policy in terms of sustainability, the authors have used indicators for environmental concentrations (PEC/PNEC ratios), for human intake (PDI/TDI ratios) and for environmental accumulation both in 1990 and in a steady-state scenario. In order to assess the level of the PEC/PNEC ratios, i.e. calculating the risk ratio for aquatic and terrestrial ecotoxicity, the Dutch Maximum Permissible Concentration (MPC) values have been applied (these values were taken from references either in Dutch language or a not readily available RIVM report). However, the MPC values, as shown in Figures III.1.5 and III.1.6, are equal to 1, i.e. the limit value for the PEC/PNEC ratio, above which an unacceptable risk for the ecosystem might be at hand. Usually the MPC value is not expressed as a ratio, but as a concentration in absolute numbers. Therefore, it is far from obvious what is meant by MPC in the present context. Maybe it is meant that the MPC value is equal to the PNEC value, but no PNEC value is given in clear number for any of the metals. Therefore, it is impossible to make a proper assessment of the validity of the reasoning by the authors. This ambiguity does not prevent the authors from using the (unspecified) MPC values in the evaluation.

The evaluation has resulted in the following conclusion: "At present, MPC values are not transgressed for any of the metals. However, in the steady state ecotoxicological risk ratios are expected to be over 1 for all metals except cadmium." In fact, from Figure III.1.5 it can be seen that the PEC/PNEC ratio for copper in the aquatic environment will increase from about 0.2 to 35.0 when we move from the 1990 situation to the steady-state scenario. The terrestrial ecotoxicity risk ratio for copper will rise from about 0.7 in 1990 to 6.7 at the steady-state situation. Again, the ratio for cadmium will increase just a little when moving from the 1990 to the steady-state situation, but never transgress the limit value of 1.0. If we assume that the PNEC value (or possibly the MPC value) for copper in the aquatic ecosystem will remain the same in the year 1990 and at a steady-state scenario, then the dramatic rise of the ratio from 0.2 to 35, i.e. rise by 175 times, must depend on an increase in the PEC value by 175 times. It is hard to understand how the doubling of total copper immission (cf. Table 3.4), or the doubling of total copper emissions (in fact an increase by 5 times in the emissions to water was calculated by the authors) from 1990 to the steady-state situation can cause a 175-fold rise in PEC. Unfortunately, it must be concluded that the data presented in the book under review simply do not stick together.

It is also interesting to note that the accumulation of copper and zinc in the environment is considered to be so fast that the transition period for risk ratios in the Dutch environment to become unacceptable is 3 and 16 years, counted from 1990, for copper and zinc, respectively, in the aquatic environment, while it is 1000 years for lead and the transition period for cadmium is eternal. These conclusions by van der Voet, Guinée and de Haes (2000) on the future environmental and health risks of copper and zinc, compared to the risk of cadmium, must be considered to have a low credibility.

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