Kristel Sniegowski

Improvement of pesticide mineralization in on‐farm biopurification systems by bioaugmentation with pesticide‐primed soil

Microcosms were used to examine whether pesticide-primed soils could be preferentially used over nonprimed soils for bioaugmentation of on-farm biopurification systems (BPS) to improve pesticide mineralization. Microcosms containing a mixture of peat, straw and either linuron-primed soil or nonprimed soil were irrigated with clean or linuron-contaminated water. The lag time of linuron mineralization, recorded for microcosm samples, was indicative of the dynamics of the linuron-mineralizing biomass in the system. Bioaugmentation with linuron-primed soil immediately resulted in the establishment of a linuron-mineralizing capacity, which increased in size when fed with the pesticide. Also, microcosms containing nonprimed soil developed a linuron-mineralizing population, but after extended linuron feeding. Additional experiments showed that linuron-mineralization only developed with some nonprimed soils. Concomitant with the increase in linuron degradation capacity, targeted PCR-denaturing gradient gel electrophoresis showed the proliferation of a Variovorax phylotype related to the linuron-degrading Variovorax sp. SRS16 in microcosms containing linuron-primed soil, suggesting the involvement of Variovorax in linuron degradation. The correlation between the appearance of specific Variovorax phylotypes and linuron mineralization capacity was less clear in microcosms containing nonprimed soil. The data indicate that supplementation of pesticide-primed soil results in the establishment of pesticide-mineralizing populations in a BPS matrix with more certainty and more rapidly than the addition of nonprimed soil.

A molecular toolbox to estimate the number and diversity of Variovorax in the environment: application in soils treated with the phenylurea herbicide linuron

Real-time PCR and PCR-denaturing gradient gel electrophoresis (DGGE) approaches that specifically target the Variovorax 16S rRNA gene were developed to estimate the number and diversity of Variovorax in environmental ecosystems. PCR primers suitable for both methods were selected as such that the enclosed sequence showed maximum polymorphism. PCR specificity was maximized by combining PCR with a targeted endonuclease treatment of template DNA to eliminate 16S rRNA genes of the closely related Acidovorax. DGGE allowed the grouping of PCR amplicons according to the phylogenetic grouping within the genus Variovorax. The toolbox was used to assess the Variovorax community dynamics in agricultural soil microcosms (SMs) exposed to the phenylurea herbicide linuron. Exposure to linuron resulted in an increased abundance within the Variovorax community of a subgroup previously linked to linuron degradation through cultivation-dependent isolation. SMs that were treated only once with linuron reverted to the initial community composition 70 days after linuron exposure. In contrast, SMs irrigated with linuron on a long-term base showed a significant increase in Variovorax number after 70 days. Our data support the hypothesis that the genus Variovorax is involved in linuron degradation in linuron-treated agricultural soils.

Robust Linuron Degradation in On-Farm Biopurification Systems Exposed to Sequential Environmental Changes

ABSTRACT On-farm biopurification systems (BPS) treat pesticide-contaminated wastewater of farms through biodegradation. Adding pesticide-primed soil has been shown to be beneficial for the establishment of pesticide-degrading populations in BPS. However, no data exist on the response of pesticide-degrading microbiota, either endogenous or introduced with pesticide-primed soil, when BPS are exposed to expected less favorable environmental conditions like cold periods, drought periods, and periods without a pesticide supply. Therefore, the response of microbiota mineralizing the herbicide linuron in BPS microcosm setups inoculated either with a linuron-primed soil or a nonprimed soil to a sequence of such less favorable conditions was examined. A period without linuron supply or a drought period reduced the size of the linuron-mineralizing community in both setups. The most severe effect was recorded for the setup containing nonprimed soil, in which stopping the linuron supply decreased the linuron degradation capacity to nondetectable levels. In both systems, linuron mineralization rapidly reestablished after conventional operation conditions were restored. A cold period and feeding with a pesticide mixture did not affect linuron mineralization. The changes in the linuron-mineralizing capacity in microcosms containing primed soil were associated with the dynamics of a particular Variovorax phylotype that previously had been associated with linuron mineralization. This study suggests that the pesticide-mineralizing community in BPS is robust in stress situations imposed by changes in environmental conditions expected to occur on farms. Moreover, it suggests that, in cases where effects do occur, recovery is rapid after restoring conventional operation conditions.

High prevalence of IncP-1 plasmids and IS1071 insertion sequences in on-farm biopurification systems and other pesticide-polluted environments

Mobile genetic elements (MGEs) are considered as key players in the adaptation of bacteria to degrade organic xenobiotic recalcitrant compounds such as pesticides. We examined the prevalence and abundance of IncP-1 plasmids and IS1071, two MGEs that are frequently linked with organic xenobiotic degradation, in laboratory and field ecosystems with and without pesticide pollution history. The ecosystems included on-farm biopurification systems (BPS) processing pesticide-contaminated wastewater and soil. Comparison of IncP-1/IS1071 prevalence between pesticide-treated and nontreated soil and BPS microcosms suggested that both IncP-1 and IS1071 proliferated as a response to pesticide treatment. The increased prevalence of IncP-1 plasmids and IS1071-specific sequences in treated systems was accompanied by an increase in the capacity to mineralize the applied pesticides. Both elements were also encountered in high abundance in field BPS ecosystems that were in operation at farmyards and that showed the capacity to degrade/mineralize a wide range of chlorinated aromatics and pesticides. In contrast, IS1071 and especially IncP-1, MGE were less abundant in field ecosystems without pesticide history although some of them still showed a high IS1071 abundance. Our data suggest that MGE-containing organisms were enriched in pesticide-contaminated environments like BPS where they might contribute to spreading of catabolic genes and to pathway assembly.

Dynamics of the Linuron Hydrolase libA Gene Pool Size in Response to Linuron Application and Environmental Perturbations in Agricultural Soil and On-Farm Biopurification Systems

ABSTRACT libA, a gene encoding a novel type of linuron hydrolase, was recently identified in the linuron-mineralizing Variovorax sp. strain SRS16. In order to assess the contribution of libA to linuron degradation in environmental settings, libA abundance was monitored in response to the application of linuron and to environmental perturbations in agricultural soil microcosms and microcosms simulating the matrix of on-farm biopurification systems. libA numbers were measured by real-time PCR and linked to reported data of Variovorax community composition and linuron mineralization capacity. In the soil microcosms and one biopurification system setup, libA numbers responded to the application of linuron and environmental changes in congruency with the modulation of linuron mineralization capacity and the occurrence of a particular Variovorax phylotype (phylotype A). However, in another biopurification system setup, no such correlations were found. Our data suggest that in the simulated environmental settings, the occurrence of libA can be linked to the linuron mineralization capacity and that libA is primarily hosted by Variovorax phylotype A strains. However, the results also suggest that, apart from libA, other, as-yet-unknown isofunctional genes play an important role in linuron mineralization in the environment.

Inverse modeling of pesticide degradation and pesticide―degrading population size dynamics in a bioremediation system: Parameterizing the Monod model

Pesticide degradation models are compared which simulate the response of biofilters for treatment of pesticide-contaminated waste water to time-irregular pesticide supply in which the pesticide is used for growth and mineralized. Biofilter microcosms containing a mixture of straw, peat and soil and harboring micropopulations which uses the herbicide linuron for growth, were irrigated with linuron for 28 weeks with a stop in its supply between week 12 and 17. Matrix samples were regularly taken to assay linuron mineralization. A first-order approximation of the Monod model was used to simulate the observed mineralization data, while an inverse modeling framework combining a sensitivity analysis (Morris Sensitivity Analysis) with an inverse modeling approach (Shuffled Complex Evolution Metropolis) adopted to parameterize the model. Lag times in linuron mineralization decreased during the initial weeks of linuron irrigation but increased after supply of linuron ceased. The model well-simulated the lag time dynamics which were related to the dynamics of the predicted linuron-degrading population size in the microcosms. It was predicted that the population size decreased at a rate of 0.031 d(-1) after pesticide supply ceased to reach its initial population size after 25 weeks. We conclude that modeling pesticide degradation in biofilters should incorporate biomass dynamics in case the pesticide is used as C-source. First-order approaches without incorporating biomass dynamics could lead to underestimation of the risk of pesticide leaching.

Minimal pesticide-primed soil inoculum density to secure maximum pesticide degradation efficiency in on-farm biopurification systems

Addition of pesticide-primed soil containing adapted pesticide degrading bacteria to the biofilter matrix of on farm biopurification systems (BPS) which treat pesticide contaminated wastewater, has been recommended, in order to ensure rapid establishment of a pesticide degrading microbial community in BPS. However, uncertainties exist about the minimal soil inoculum density needed for successful bioaugmentation of BPS. Therefore, in this study, BPS microcosm experiments were initiated with different linuron primed soil inoculum densities ranging from 0.5 to 50 vol.% and the evolution of the linuron mineralization capacity in the microcosms was monitored during feeding with linuron. Successful establishment of a linuron mineralization community in the BPS microcosms was achieved with all inoculum densities including the 0.5 vol.% density with only minor differences in the time needed to acquire maximum degradation capacity. Moreover, once established, the robustness of the linuron degrading microbial community towards expected stress situations proved to be independent of the initial inoculum density. This study shows that pesticide-primed soil inoculum densities as low as 0.5 vol.% can be used for bioaugmentation of a BPS matrix and further supports the use of BPS for treatment of pesticide-contaminated wastewater at farmyards.

Establishment of multiple pesticide biodegradation capacities from pesticide-primed materials in on-farm biopurification system microcosms treating complex pesticide-contaminated wastewater.

BACKGROUND On-farm biopurification systems (BPSs) treat pesticide-containing wastewater at farms by biodegradation and sorption processes. The inclusion of pesticide-primed material carrying a pesticide-degrading microbial community is beneficial for improving biodegradation, but no data exist for treating wastewater containing multiple pesticides, as often occurs on farms. In a microcosm set-up, an examination was carried out to determine whether multiple pesticide degradation activities could be simultaneously established in the matrix of a BPS by the simultaneous inclusion of different, appropriate pesticide-primed materials. The microcosms were fed with a mixture of pesticides including the fungicide metalaxyl and the herbicides bentazon, isoproturon, linuron and metamitron, and pesticide-degrading activities were monitored over time. RESULTS The strategy immediately provided the microcosms with a multiple pesticide degradation/mineralisation capacity, which improved during feeding of the pesticide mixture. Not only did the degradation of the parent compound improve but also that of the produced metabolites and compound mineralisation. The time to achieve maximum degradation/mineralisation capacity depended on the pesticide degradation capacity of the pesticide-primed materials. CONCLUSIONS The data obtained show that the addition of pesticide-primed materials into the matrix of a BPS as an approach to improve biodegradation can be extended to the treatment of pesticide mixtures.

AOX removal from industrial wastewaters using advanced oxidation processes: assessment of a combined chemical–biological oxidation

In this paper, the abatement of adsorbable halogenated organic compounds (AOX) from an industrial wastewater containing relatively high chloride concentrations by a combined chemical and biological oxidation is assessed. For chemical oxidation, the O(3)/UV, H(2)O(2)/UV and photo-Fenton processes are evaluated on pilot scale. Biological oxidation is simulated in a 4 h respirometry experiment with periodic aeration. The results show that a selective degradation of AOX with respect to the matrix compounds (expressed as chemical oxygen demand) could be achieved. For O(3)/UV, lowering the ratio of O(3) dosage to UV intensity leads to a better selectivity for AOX. During O(3)-based experiments, the AOX removal is generally less than during the H(2)O(2)-based experiments. However, after biological oxidation, the AOX levels are comparable. For H(2)O(2)/UV, optimal operating parameters for UV and H(2)O(2) dosage are next determined in a second run with another wastewater sample.

Potential of activated carbon to recover randomly-methylated-β-cyclodextrin solution from washing water originating from in situ soil flushing

Despite the overall high efficacy of cyclodextrins to accelerate the treatment of soil aquifer remediation by in-situ soil flushing, the use in practice remains limited because of the high costs of cyclodextrin and high concentrations needed to significantly reduce the treatment time. The current study tested the potential of activated carbon to treat washing water originating from soil flushing in order to selectively separate hydrocarbon contaminants from washing water containing cyclodextrin and subsequently reuse the cyclodextrin solution for reinfiltration. A high recovery of the cyclodextrin from the washing water would reduce the costs and would make the technique economically feasible for soil remediation. This study aimed to investigate whether cyclodextrin can pass through the activated carbon filter without reducing the cyclodextrin concentration when the contaminated washing water is treated and whether the presence of cyclodextrin negatively affects the purification potential of activated carbon to remove the organic pollutants from the pumped soil water. Lab-scale column experiments showed that with the appropriate activated carbon 100% of cyclodextrin (randomly-methylated-β-cyclodextrin) can be recovered from the washing water and that the effect on the efficiency of activated carbon to remove the hydrocarbon contaminants remains limited. These results show that additional field tests are useful to make in-situ soil flushing with cyclodextrin both a technical and an economical interesting technique. These results might stimulate the application of cyclodextrin in soil treatment technology.