Development of a field bioassay for the side-effects of herbicides on vascular plants using Brassica napus and Poa annua.

A field bioassay method has been developed for assessing side-effects of herbicides on Brassica napus and Poa annua. The test method aims at effects outside the target area, up to 20 m from the treated parcel. Experiments were conducted in the field and in a glasshouse with the herbicides atrazin, bentazone, diquat, glyphosate, and r(4-chloro-2-methylphenoxyacetic acid) MCPA. An iterative procedure was used with the aim of developing a sound test procedure. The resulting method appeared to be very sensitive. Pesticide drift was measured using water-sensitive paper. Effects were sometimes found below the detection limit of this method (at 8 m from the treated parcel with moderate wind speeds of 3-5 m/s). The sensitivity of the test and the test conditions are discussed and an optimized method is presented.

Effects of glufosinate-ammonium on off crop vegetation--interim results.

In 2000 a field study was conducted at four different locations concerning the effects of low dosages of glufosinate-ammonium, a leaf acting herbicide, on off crop vegetation. Therefore species rich road verges and ditch banks not adapted to a history of herbicide use were sprayed twice with different dosages of glufosinate-ammonium, simulating drift (0, 2, 4, 16, 32 and 64% of the maximum field dose: 800 g a.i./ha). The parameters studied were short term phytotoxic effects and the effects on biomass, species cover and number of species in autumn (Braun-Blanquêt relevés). The results show significant phytotoxic effects at all dosages of glufosinate-ammonium on the non-target vegetation. The low concentrations (2 and 4%) had most impact when applied early in the season (9% average at the 2% dosage and 22% at 4% dosage, after the first spraying. At high dosages (32 and 64%) a decrease of the biomass of the vegetation was found in August. A comparison between treatments in August shows a small decrease in species number and cover in the 64% compared to the control. In the comparison between the spring and August relevés, the decrease in the mean number of species was significantly stronger in the treated plots than in the untreated ones of 4% and higher. For monocotyledons in all treatments except 16%, a significantly stronger decrease in species number was found compared to the untreated. For dicotyledons only the 64% dosage differed from the untreated. Only at the 64% treatment the total cover of species decreased more than in the untreated plots. Since drift percentages of 2-4% can be expected at 1-2 m from a treated plot it can be concluded that the use of glufosinate-ammonium could result in visible short term phytotoxic effects (max 22%) on off-crop vegetation such as ditch banks and verges. There are also indications that effects on the number and cover of species in autumn can occur. Because in future glufosinate-ammonium could be used on a large scale in herbicide resistant crops like maize, which will be cultivated on the same field for many years, this study will be continued in 2001 in order to investigate if there are--whether or not--sustainable effects on the off crop vegetation.

Trends of pesticide use in The Netherlands.

In 1991, a policy plan was adopted in the Netherlands, one of whose aims was a 50% reduction in pesticide use by 2000. The present paper surveys pesticide sales since 1974 and the use of such compounds in different crops per hectare as well as for the country as a whole. The results show that by the mid-1990s, pesticide consumption in kilogram terms had been reduced by about 50% compared to the mid-1980s. This reduction, however, was almost totally caused by the reduction in the use of soil disinfectants, while reduction targets for herbicides and fungicides were not met at all. Arable crops, especially potatoes and maize, which cover large areas in the Netherlands, contributed most to total consumption, while apples, tulips and lilies also made considerable contributions. On a per hectare per year basis, pesticide consumption was highest in ornamental plants like roses, chrysanthemums, lilies and hyacinths, followed by vegetables grown in greenhouses, apples and pears and mushroom cultivation. A remarkable feature is that the majority of the 20 most commonly used compounds (in terms of total consumption in kilograms of active ingredient or area sprayed) had already been introduced before 1980. On a kilogram basis, fungicides and soil disinfectants were used in the largest quantities, together with mineral oil and followed by herbicides. On a per hectare basis, herbicides played a more important role, while one insecticide also featured.

Pesticide residues in human food and wildlife in The Netherlands.

Several monitoring programmes for pesticide residues in food are currently operative in the Netherlands, some of which are related to EU directives. These programmes cover a range of products. This paper reviews the 1997 and 1998 data for fruit and vegetables, meat, milk, livestock and fish, as well as presenting data on pesticide residues in wildlife. The aim of the paper is to provide an overview of what is known about pesticide residues in the Netherlands, including indications of the origins of the compounds found. A total of 281 different compounds were monitored on fruit and vegetables. Of these compounds, 45% were actually found on products and 28% exceeded the standard. Expressed as percentages of the number of measurements, the data show that 0.3% of the measurements detected a compound, and standards were exceeded in 0.02% of the measurements. Some of the cases in which standards were exceeded concerned the use of compounds in minor crops, for which their use is not permitted. Other cases involved excessive dosages or application within the safety interval before harvest. In meat, milk and livestock, 10 persistent organochlorine compounds were measured. Most of these compounds, with the exception of lindane, are no longer in use, but are still being found as residues. The concentrations found were very low and have not exceeded standards for human consumption since 1993. No assessment was made, however, of products currently in use. Organochlorine compounds have also frequently been found in fish (eel), in higher concentrations than in meat, but in nearly all cases in quantities below the standards for human consumption. Ecological standards for accumulation in the food chain were exceeded on a larger scale and indications of exposure effects on piscivorous birds (cormorants) were found. No data on pesticide residues in wildlife are known for terrestrial organisms.

Field research for the authorisation of pesticides.

On request of the Dutch government a committee of the Health Council of the Netherlands has reviewed the role that results of field research in its broadest sense (i.e., including multi-species toxicity tests in the laboratory, research on model ecosystems et cetera) can play in ecotoxicological risk assessment for the authorisation of pesticides. The Committee believes that field research can provide valuable additional data about the exposure of non-target organisms and the resultant effects at population, community and ecosystem level. However, it frequently is unclear how these data might be used in reaching a decision about authorisation. To solve this problem, it is necessary to specify what is understood by "unacceptable damage". Both more clearly formulated protection goals of the government and a better understanding of the ecological significance of effects are needed to clarify this. Furthermore, the Committee points out that the statistical power of field trials must be sufficient to allow for the detection of changes that might be regarded as ecologically relevant. Finally, it recommends keeping a finger on the pulse in relation to authorised pesticides by monitoring their presence in environmental compartments and by investigating their role in suddenly occurring mortality among conspicuous animal species, such as birds, fish and honeybees. This kind of research forms a safety net for substances that have been wrongly authorised.

Development of a field bioassay for the side effects of pesticides on decomposition.

A method has been developed for assessing the side effects of fungicides on decomposition using litterbags. Twenty dried leaf disks of Chinese cabbage, Brassica oleracea, were placed in litterbags (20 x 20 cm) made of nylon fabric (25 microns mesh). The litterbags were laid in a treated plot and 5, 10, 20, and > 200 m from the treated plot and covered with 1 cm of standard soil. After 1 week, the dry weight of the leaf disks was determined. In an iterative procedure the method was optimized and significant differences of 5% in decomposition rate between litterbags were found using the final method presented here. In and around agriculturally managed plots, negative effects on decomposition of two fungicides could be traced. Effects on decomposition were found after application of captan (in fruit, 1.5 kg a.i./ha) and maneb (in potatoes, 3 kg a.i./ha) up to 10 m from the treated plot, at moderate wind speeds (3-5 m/s). In one case the concentration of captan in the soil covering the litterbags was measured. A negative correlation was established between captan concentration and decomposition. These experiments were repeated in an experimental plot under more controlled conditions with respect to the amount and time of application. The results of the field experiments could not be reproduced on the experimental plot. Additional experiments with soil fungi in agar again demonstrated a significant effect of exposure to captan, however. Given the results, the method using litterbags requires further development before a standard field trial can be designed. Given the knowledge gained with respect to the key factors involved, a bioassay using soil fungi seems to have high potential, however.

Possible side effects of airborne pesticides on fungi and vascular plants in The Netherlands.

A survey of the potential side effects of volatilized pesticides on fungi and vascular plants in The Netherlands has been made for two herbicides (atrazine and MCPA), a fungicide (captan) and a soil fumigant (metham sodium). By applying existing models, a prediction is presented of post-treatment dispersal and deposition due to volatilization, both at short and long ranges, and of the potential side effects on fungi and vascular plants. The general conclusion is that side effects (stunting and growth anomalies) are to be expected outside the target area, especially close (< 500 m) to treated plots with atrazine and metham sodium. In view of agricultural acreage in The Netherlands, these short-range effects may impinge on a relatively large scale. There may also be an impact at greater distances from treated plots, especially in the case of compounds that are slow to degrade such as MITC (methyl isothiocyanate), the active toxic moiety generated in soil from metham sodium.