Biodegradation of pesticides by adapted fungi. Potential use on biopurification systems?

Abstract

Biopurification systems (BPSs) constitute a valuable approach to mitigate/reduce the contamination of water sources with pesticides. These systems employ the degrading capacity of a biomixture to avoid/minimize, in a simple and low cost way, the pollution of discharging of pesticide-containing wastewater in the aquatic environment.

Therefore processes and parameters controlling depuration ability of BPSs should be a priority research issue due to the lack of alternative treatments.

The aim of this work was to evaluate the performance of three fungi, selected and isolated from different primed materials, to biodegrade the pesticides terbuthylazine, difenoconazole, diflufenican, and pendimethalin, in a biomixture containing soil and cork as substrate. Experiments using only sterilized soil were carried out as control. Each fungus species was inoculated individually (in the biomixture or soil), and their ability to biodegrade the target pesticides was evaluated during 120 days.

All the fungi strains inoculated (Fusarium oxysporum PP0030, Paecilomyces variotii PP0040, and Trichoderma viride PP0050), proved to be valuable as active pesticide-degrading microorganisms, demonstrating a very high biotransformation ability of the target pesticides, particularly in the biomixture.

F. oxysporum PP0030 generally biodegraded higher amounts of the pesticides terbuthylazine, difenoconazole, and diflufenican, followed by P. variotii PP0040 and T. viride PP0050. After 120 days, maximum biodegradation of terbuthylazine, difenoconazole, and diflufenican, in inoculated biomixture with F. oxysporum PP0030, was 89.4%, 81.5%, and 74.7%, respectively. Moreover, a biodegradation for pendimethalin close to 100% was achieved by all fungi.

This paper is also a breakthrough in the understanding of the metabolic pathways used by fungi to biodegrade pesticides. With the results presented, it seems to be clear that the metabolization of terbuthylazine by fungi follows different metabolic routes in different media, leading to the production of different metabolites. This conclusion had already been advanced in our previous studies, using the white-rot fungus Lentinula edodes, being now reiterated and confirmed with different fungi species.

In this study, it was also possible to identify a pendimethalin metabolite that had already been indicated as a degradation product of this herbicide by bacteria, but as far as we know, it was never described as an intermediate metabolite of pendimethalin biotransformation by fungi.

Sorption process to cork by pesticides studied proved to be a reversible process, which potentially allows the complete biodegradation of the pesticides. This reversibility of the pesticides’ sorption processes on cork establishes that the use of these biomixtures can reduce the amount of contaminated waste by using the same substrate in successive applications of wastewaters, increasing the sustainability of the system.

In conclusion, our results are very useful and can be used as important data in the construction of sustainable BPS, suitable for the depuration and detoxification of wastewaters containing the target pesticide or other with similar intrinsic characteristics, contributing to the protection of aquatic resources as well as maintaining their quality and reducing the wastes.