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Fate and toxicity of allelochemicals (natural plant toxins) in relation to environment and consumer

In recent years, there has been an increasing focus on the prospects of exploiting allelopathy as an alternative strategy for controlling weeds, insects and diseases. However, the environmental and toxicological consequences of this should be investigated. Well-described allelopathic properties of wheat combined with low environmental persistence and low toxicities should enhance the possibilities for farmers to make a sound assessment. If the evaluation of environmental persistence and human, as well as environmental, toxicities shows that the allelochemical compounds constitute a higher risk than the risk of low doses of synthetic pesticides, new views must be put forward on exploiting allelopathy.

The objective of the project is to perform an environmental and human risk assessment of exploiting the allelopathic properties of wheat in modern farming and to develop a framework for future assessments of allelopathic crops. This will be reached through the fulfilment of the following objectives:
1) to quantify the amount of allelochemicals and their metabolites in a) wheat of
different origins and grown under different environmental conditions and b) in the
surrounding soil environment
2) to generate dose-response relationships of major wheat allelochemicals on important target weeds and pests
3) to assess the risk to environment and consumers of wheat allelochemicals and their metabolites in comparison with synthetic pesticides
4) to compare the empirical results with theoretical results using rules-based prediction of toxicity and rule-based prediction of environmental transformation.

Progress to Date
So far, the studies on herbicidal effects on pot experiments and with incorporated plant material has not revealed any significant differences between the chosen varieties. However, the pot experiments suffered from a very poor germination of some of the weed seeds, and the experiments incorporating high amounts of plant material in soil showed difficulties in obtaining the contact between soil and weed seed required for germination. The EQAM revealed that only living plants were allelopathic. When comparing the results on insecticidal effects, herbicidal effects and bioassays no general conclusion can be made so far. Different wheat allelochemicals has more influence on weeds than on insects and vice versa, and the matrixes in which the trials are performed can lead to transformations of the hydroxamic acids that vary between the matrixes.

A new view on research into benzoxazinoids, allelochemicals from wheat, was launched in the FATEALLCHEM project ( The overall objective was to perform an environmental and human risk assessment of exploiting the allelopathic properties of wheat in modern farming and to develop a framework for future assessments of allelopathic crops.
The development of analytical methods in LC-MS or LC-MS/MS for benzoxazinoids in plants and soil, which has hardly been considered in earlier research, was complicated. Sensitive methods were developed and the first intercalibration study ever on the analytical procedures for analyzing benzoxazinoids in plant material was published recently. The analysis of different varieties of wheat showed that there is a genetic difference between varieties in the level of production of defence compounds as well as environmental effects on the levels. Benzoxazinoids were shown to degrade very rapidly in soil with DT50 values £1-2 days. The formation of degradation products depended on the initial concentration of the benzoxazinoids in soil or test media. Several transformation products showed more pronounced suppressive effects on both weeds and fungi than the parent compound. The conclusions in earlier published studies, in which the effect of wheat benzoxazinoids on weeds or soil-borne diseases have been studied without any focus on the transformation that occurred during the time of study must now be revised.
Toxicological evaluations on benzoxazinoids and their soil metabolites were performed for the first time in this project. The ecotoxicological studies showed that the soil transformation products with highest suppressive effects on weeds and fungi also had the highest toxicological effects on beneficial organisms (carabid beetle larvae, collembola and selected aquatic organisms). However, the harmful effects of the most bioactive metabolites did not exceed negative effects of synthetic pesticides. QSAR studies on human and mammal toxicity showed that harmful effects on humans or animals consuming high concentrations of the benzoxazinoids should be taken into consideration.The project results clearly showed the relevance of optimizing the exploitation of cereal benzoxazinoids. Crop rotation is a very traditional practice, which was given less importance for decades, but now is regaining its importance in agricultural practice as a means of controlling weed seed banks and soil-borne diseases and pests. Cover crops and green manure are used more extensively in modern sustainable agriculture as well. When using cereals as catch crops and green manure, the allelopathic properties of the cereals could now be much more extensively exploited, choosing varieties with optimal production of benzoxazinoids and optimizing the time of sowing in relation to the formation of bioactive metabolites. A framework for future assessments of an extensive use of allelopathic crops must include the development of validated analytical methods, considerations of relevant concentrations, studies on soil transformation, ecotoxicological studies on individual compounds and mixtures, evaluation on human and mammal toxicity and joint effect studies on weeds, fungi and pests.


Scientist responsible for the project

Research Centre Flakkebjerg
4200 Slagelse
Denmark - DK

Phone: +45 58113410
Fax: +45 58113301


Project ID QLRT-2000-01967
Organisation Danish Institute of Agricultural Sciences, Department of Crop Protection
Area 5.1.1
Start date 01 September 2001
Duration (months) 36
Total cost 2 662 537 €
Total EC contribution   1 571 337 €
Status Completed
Web address of the project

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