Chapter 18
Lysimeter Data in Pesticide Authorization H.-G. Nolting and K. Schinkel
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Biological Research Center for Agriculture and Forestry, Department of Plant Protection Products and Application Techniques, Chemistry Division, Braunschweig, Germany
The assessment of the mobility of plant protection products in soil is a very important part within the authorization procedure for pesticides in the Federal Republic of Germany. In recent years lysimeter studies have been proven to be the best methods to assess the probability of pesticides entering into ground water. For substances with a DT value of more than 21 days and an adsorption constant Koc of less than 500, computer-aided model calculations at realistic worst case conditions are first conducted. If a concentration of 0.1 μg/l or more is calculated, lysimeter studies have to be carried out. An authorization of the plant protection product is only granted if the concentration of the active substance in the leachate is less than 0.1 μg/l averaged over one year. The lysimeter concept was also adopted by the E U Directive 91/414/EEC where in special cases lysimeter or field studies for the assessment of the mobility of active substances are required. In the last few years lysimeter studies were conducted for more than 40 active substances within the German authorization procedure. 50
First an overview on the role of lysimeter studies within the authorization procedure and the requirements for the necessity of carrying out such studies shall be given. To prevent an unjustifiable contamination of ground water, within the authorization procedure of plant protection products in Germany, information on the degradability and mobility of the active substance in soil is needed to be able to assess the possibility of ground water contamination. The basis for these requirements is the German Plant Protection Act of 1986 which states in Article 15 that an authorization can only be granted if the plant protection product "...does not have any harmful effects on human and animal health or on ground water.".
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©1998 American Chemical Society
Führ et al.; The Lysimeter Concept ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
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Unfortunately, the legislator failed to give a definition of the term "harmful effects". Therefore, in 1989 the Federal Biological Research Center for Agriculture and Forestry (BBA) decided, in agreement with the Federal Environmental Agency (UBA), that a harmful effect must be assumed, and that therefore an authorization must be refused, if in the investigation of the mobility of the active substance it seems that concentrations in ground water of 0.1 μg/l or more could be expected. This decision was confirmed within two court proceedings at the Administrative Court in Braunschweig in 1990, where it was said that "the entry of an active substance into ground water then leads to inadmissible effects if after the proper use of the respective plant protection product, the limit of the Drinking Water Ordinance of 0.1 pg/l is reached or exceeded". The assumption as to what concentrations of pesticides in ground water could be expected is based on results of lysimeter studies.
Advantages of Lysimeters Among the different methods for the estimation of the mobility of active substances in soil, lysimeter studies are regarded up to now to be most reliable, because such trials enable the use of undisturbed soil cores and, of particular importance, the application of radioactively labelled test material. The advantages of lysimeter studies versus laboratory leaching studies are obvious (7): • They are performed under real environmental conditions, e. g. natural precipitation, sunshine, air and soil temperatures. • Use of a natural soil profile instead of repacked soil columns in the laboratory. • The possibility of cultivation of the lysimeter surface according to good agricultural practice. • Microbially active soils; soils for laboratory studies are often air-dried prior to use. • Realistic soil depth thus taking into account the change in the degradation rate with downward movement of the active substances. Even in comparison with field studies there are considerable advantages: • The possibility of using radioactively labelled test material. The use of radioactively labelled material in field studies is usually prohibited. • The possibility of comparison of different soil types. • An easy and comparable study management, e. g. the location of different lysimeters at the same facility ensures identical management practices. • The possibility of artificial irrigation. • The sampling of the total leachate; all water draining through the profile can be collected for analysis thus allowing a tentative mass balance
Führ et al.; The Lysimeter Concept ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
240 Necessity of Lysimeter Studies However lysimeter studies are not necessary in every case in the course of the German authorization procedure. The decision on whether such studies are necessary or not might be made by using the flow diagram shown in Figure 1. If the degradation rate of the respective active substance shows a D T value (lab.) of less than 21 days and an adsorption constant of more than 500 with regard to the safety of ground water, an authorization can be granted, because the probability of a penetration into deeper soil layers by normal leaching events would be minimal. If the D T value exceeds 21 days and the value is less than 500, computer-aided model calculations have to be conducted first, taking into account realistic worst case conditions. Within the Member States of the E U , different calculation models are used, e.g. in the Netherlands the PESTLA model is preferred, whereas in Germany the P E L M O model is regarded to be the most appropriate model. In most cases, the calculation covers a period of 10 years. If the P E L M O calculation shows a simulated concentration of 0.1 μg/l or more in ground water for at least one year, lysimeter studies have to be conducted. It must be stressed that modelling results are used as triggers for the necessity of lysimeter studies and not as cutoff triggers. A comparison between lysimeter and P E L M O results (on the basis of 39 lysimeter cores, 14 active substances, 1 metabolite) which was conducted by order of the German Agrochemicals Association (IVA) and the Federal Environmental Agency (UBA) (2) showed that the P E L M O calculations are appropriate to estimate the probability of ground water contamination. 50
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50
Lysimeter Studies The conditions under which lysimeter studies should be conducted are laid down in a BBA-Guideline (3). In these experiments, an undisturbed soil core of 1.0 - 1.2 m depth and a surface of 0.5 - 1.0 m should be used. The soil should be a light sandy soil with a content of at least 70 % sand, at the most 10 % clay and not more than 1.5 % organic carbon. The preparation of the active substance which should be radioactively labelled is applied in the highest intended amount and at the intended time. A precipitation rate of at least 800 mm per year must be maintained, possibly by irrigation. The experiment is conducted over a period of at least 2 years but in some cases up to 4 years. During this time, the lysimeter is cultivated according to good agricultural practice. The percolated water is sampled from time to time and analyzed for the contents of total radioactivity, parent compound, metabolites and unidentifiable radioactive residues. At the end of study, the soil core from the surface to the bottom is divided into 10-cm layers, and each layer is also analyzed for total radioactivity, parent compound, metabolites and bound residues, thus illustrating the distribution of the different fractions in the whole soil core and giving additional information about the degradability and degree of adsorption of the compound and its metabolites to soil particles. According to the lysimeter results submitted up to now, it seems that only in the upper 20-cm soil layer was the concentration of extractable radioactivity high 2
Führ et al.; The Lysimeter Concept ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
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DT 50 500 ? (a.i.and main metabolite (s)*) >
yes
Model calculation; realistic „worst case" scenario
c0.1
- 4% ~ 8% ~ 8% 0%
From these positive results, it could be concluded that lysimeter studies will always have positive results, i. e. never exceeding the 0.1 μg/l value in the leachate, for every active substance, but it isn't like that. Because the applicants know that an authorization is not granted if in a lysimeter study the 0.1 pg/l value is exceeded, they may refrain from submitting an application for authorization for pesticides that are too mobile and too persistent.
Metabolites and Nonidentifiable Radioactivity In contrast to the positive results for the parent compounds, metabolites and nonidentifiable radioactivity (NIR) often were detected in concentrations above 0.1 μg/l. Table II shows typical results from two lysimeter studies: Main metabolites in Germany (and in the EU) have been defined conventionally to be those degradation products which occurred in degradation studies in concentrations of 10 % or more, relative to the initial radioactivity, at any time of the study. If main metabolites or NIR's are found in the lysimeter percolate in concentrations of 0.1 μ%/1 or more - averaged over one year - an authorization is only granted if it can be shown that these concentrations are not harmful to human and animal health, nor to aquatic organisms (fish, daphnia, algae). If the No Observed Effect Concentrations (NOEC's) are 1000 times higher than the concentrations of metabolites in the percolates, an authorization can be granted. Examples are shown in Table II. Unfortunately, not all problems regarding possible water contamination can be solved by lysimeter studies, particularly the problem of fast flow processes under field conditions, e.g. through holes from roots or worms, and particularly through soil cracks which may be formed in periods of warm and dry weather. These problems cannot be solved within the authorization procedure nor by experiments. This is a political question. One can either accept such potential contaminations or one has to ban almost all agricultural chemicals. Furthermore, objections are sometimes raised that lysimeter studies cannot cover leaching in all types of soil under agricultural use. However, the conditions used for lysimeter studies in the German authorization procedure are "realistic worst case conditions", and we believe that these results cover the majority of situations with regard to different soil types and weather conditions in Europe. With the procedure practised in Germany regarding the problem of ground water, the problem is considered to be under control, since pesticides which may reach
Führ et al.; The Lysimeter Concept ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
244 Table IL Exemplary Lysimeter Results of Pesticides and their Main Metabolites Year
Lysimeter (Concentration in the Percolate μg/l) Pesticide
Main Metabolite 1
Main Metabolite 2
0 1 . Year
0.06
2.35
0.04
0 2. Year
0.05
0.79
0.74
0 1. + 2. Year
0.05
1.42
0.45
Ecotoxicity (NOEC-valucs)
Metabolite 1: Metabolite 2:
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Year
1. Lysimeter (Cone. Percolate μg/l)
Daphnia magna Rainbow trout Daphnia magna Rainbow trout
100 ing/l 100 nig/1 25 mg/1 5 mg/1
2. Lysimeter (Cone. Percolate jtg/I)
Pesticide
Metabolite 1
Metabolite 2
Pesticide
Metabolite 1
Metabolite 2
0 1.
