Indigenous biobed to limit point source pollution of imidacloprid in tropical countries

Laboratory and Field Studies on Bioremediation of Point-source Contamination in Horticultural Crops Using Biobeds

Biobeds are technological tools to minimize point-source contamination on productive farms. A four-step workflow for the efficient setting of biobeds in farms and its proof-of-concept is presented: (1) developing a fit-for-purpose pesticide multiresidue analytical method for pesticides in biomatrix; (2) launching biobeds at lab scale for pesticide degradation evaluation; (3) setting up the biobeds in the field; (4) evaluating the pesticide degradation in the biobed during an agricultural year. An ethyl acetate/sodium tetraborate multiresidue method was adapted and validated for 35 pesticides in the biomixture; lab biobeds were installed, and the degradation of 11 pesticides was confirmed. Then, biobeds were installed in two horticultural farms of different productive profiles, considering farmers' conditions, and included in the farmers' routine work. High dissipation rates (∼80%) in both bioreactors were observed for 10 pesticides. This research studies the performance of biobeds in reducing point source contamination and diminishing pesticide concentration from contaminated machinery washings not only at the lab scale but also at in-field experiments performed in productive farms. Moreover, the evaluation of biobeds in actual conditions where different chemical families of pesticides were applied together and the confirmation that repeated applications and accumulation of some compounds throughout the cycle proved biobeds' versatility in diminishing the point of pesticide contamination in farms.

Prevention and management of plant protection product transfers within the environment: A review

The intensification of agriculture has promoted the simplification and specialization of agroecosystems, resulting in negative impacts such as decreasing landscape heterogeneity and increasing use of plant protection products (PPP), with the acceleration of PPP transfers to environmental compartments and loss in biodiversity. In this context, the present work reviews the various levers for action promoting the prevention and management of these transfers in the environment and the available modelling tools. Two main categories of levers were identified: (1) better control of the application, including the reduction of doses and of PPP dispersion during application thanks to appropriate equipment and settings, PPP formulations and consideration of meteorological conditions; (2) reduction of post-application transfers at plot scales (soil cover, low tillage, organic matter management, remediation etc. and at landscape scales using either dry (grassed strips, forest, hedgerows and ditches) or wet (ponds, mangroves and stormwater basins) buffer zones. The management of PPP residues leftover in the spray tanks (biobeds) also represents a lever for limiting point-source PPP pollution. Numerous models have been developed to simulate the transfers of PPPs at plot scales. They are scarce for landscape scales. A few are used for regulatory risk assessment. These models could still be improved, for example, if current agricultural practices (e.g. agro-ecological practices and biopesticides), and their effect on PPP transfers were better described. If operated alone, none of the levers guarantee a zero risk of PPP transfer. However, if levers are applied in a combined manner, PPP transfers could be more easily limited (agricultural practices, landscape organization etc.).

Influence of combined application of tetracycline and streptomycin on microbial diversity and function in rice soil

A microcosm experiment was performed to quantify the residues of antibiotics [tetracycline (TC), streptomycin (STR), and streptocycline (STC; a mixture of TC and STR)] in rice soil and to assess their impact on microbial community structure and function using Illumina-MiSeq metagenomic analysis. Antibiotics were applied at half the recommended dose (0.5RD), recommended dose (RD), and double the recommended dose (2RD). At RD, TC was degraded in soil within 9 days of its application, whereas it took 21 days for STR and STC to degrade below limit of quantification (LOQ) level. The residue data were fitted in decay models, and half-lives (DT50) were 46.5-53.3 h and 177.6-198 h for TC and STR, respectively. Soil enzyme activities (dehydrogenase, β-glucosidase, fluorescein diacetate hydrolase, acid phosphatase, alkaline phosphatase) were negatively affected in the antibiotic-treated soil. Targeted metagenomic analysis showed that the major bacterial phyla such as Chloroflexi, Actinobacteria, Planctomycetes, Crenarchaeota, and Gemmatimonadetes were suppressed by antibiotic treatments as compared to control. Shannon, Simpson, ACE, and Chao1 diversity indices showed that bacterial diversity decreased with the application of antibiotics, and decrease in bacterial diversity was more prominent in case of STC as compared to TC and STR. Overall, the combination of antibiotics negatively affected the soil microbial community structure and function in comparison to their individual application.

Sustainable indigenous bio-mixture for restoration the soil point source pollution with special reference to chlorpyrifos

Improper pesticide handling is the main cause of contamination of the environment in agricultural systems. This could be caused by leakage of spraying liquid, leftovers, and inappropriate washing of spraying equipment. This study assessed the ability of suggested biomixture modules for remediate repetitive cycles of high chlorpyrifos doses. In three consecutive treatments, four tested modules were contaminated with 160 µg g-1 chlorpyrifos. Chlorpyrifos residues, dehydrogenase activity, and microbial respiration were continuously monitored for 22 weeks. Six bacterial consortia were isolated at the end of the experiment from four treated modules (B+3, BF+3, S+3, and SF+3) and two from untreated modules (B and S). The isolated consortium efficiency in degrading chlorpyrifos was studied. The results revealed that the best chlorpyrifos removal efficiency was achieved when using the stimulated biomixture module (BF) recorded 98%, 100%, and 89%, at the end of three chlorpyrifos treatments, respectively. Such removal efficiency was compatible with the biological activity results of the tested modules: dehydrogenase activity and microbial respiration. There was no difference in the efficiency among the S, B, and BF+3 consortia. The results presented here demonstrate that the combination of vermicompost, wheat straw, soil, and NPK (stimulated biomixture module) can successfully reduce the risk of a point source of pesticide pollution.

Potential of silicon-rich biochar (Sichar) amendment to control crop pests and pathogens in agroecosystems: A review

We reviewed the potential of silicon (Si)-rich biochars (sichars) as crop amendments for pest and pathogen control. The main pathosystems that emerged from our systematic literature search were bacterial wilt on solanaceous crops (mainly tomato, pepper, tobacco and eggplant), piercing-sucking hemipteran pests and soil-borne fungi on gramineous crops (mainly rice and wheat), and parasitic nematodes on other crops. The major pest and pathogen mitigation pathways identified were: i) Si-based physical barriers; ii) Induction of plant defenses; iii) Enhancement of plant-beneficial/pathogen-antagonistic soil microflora in the case of root nematodes; iv) Alteration of soil physical-chemical properties resulting in Eh-pH conditions unfavorable to root nematodes; v) Alteration of soil physical-chemical properties resulting in Eh-pH, bulk density and/or water holding capacity favorable to plant growth and resulting tolerance to necrotrophic pathogens; vi) Increased Si uptake resulting in reduced plant quality, owing to reduced nitrogen intake towards some hemi-biotrophic pests or pathogens. Our review highlighted synergies between pathways and tradeoffs between others, depending, inter alia, on: i) crop type (notably whether Si-accumulating or not); ii) pest/pathogen type (e.g. below-ground/root-damaging vs above-ground/aerial part-damaging; "biotrophic" vs "necrotrophic" sensu lato, and corresponding systemic resistance pathways; thriving Eh-pH spectrum; etc.); iii) soil type. Our review also stressed the need for further research on: i) the contribution of Si and other physical-chemical characteristics of biochars (including potential antagonistic effects); ii) the pyrolysis process to a) optimize Si availability in the soil and its uptake by the crop and b) to minimize formation of harmful compounds e.g. cristobalite; iii) on the optimal form of biochar, e.g. Si-nano particles on the surface of the biochar, micron-sized biochar-based compound fertilizer vs larger biochar porous matrices.

Microbial growth in biobeds for treatment of residual pesticide in banana plantations

Background

High doses of ethylenebisdithiocarbamate (EBDC) are used in banana production, and unused pesticide mixture (solution) is often disposed of improperly. This can result in soil and water contamination and present an undue risk to rural communities and the environment. An alternative to reduce the environmental impacts caused by pesticide residues is the biobeds treatment. It is necessary to establish if the composition of the proposed biomixtures supports microbial activity to degrade pesticides in biobeds. This research aimed to evaluate the EBDC effect on the distribution and abundance of microbial populations in polluted biomixtures .

Methods

For this purpose, a biomixture based on banana stem, mulch, and Fluvisol soil (50:25:25% v/v) was prepared and polluted with 1,000 mg L^-1 EBDC. The response variables kinetics were determined every 14 days for three months, such as pH, organic matter, moisture, cation exchange capacity, microbial colonies, and cell counts at three depths within the experimental units.

Results

EBDC reduced the number of microbial colonies by 72%. Bacterial cells rapidly decreased by 69% and fungi 89% on the surface, while the decrease was gradual and steady at the middle and bottom of the biobed. The microbial populations stabilized at day 42, and the bacteria showed a total recovery on day 84, but the fungi slightly less. At the end of the experiment, the concentration of EBDC in the biomixture was 1.3-4.1 mg L^-1. A correlation was found between fungal count (colonies and cells) with EBDC concentration. A replacement of the biomixture is suggested if the bacterial population becomes less than 40 × 10⁶ CFU mL^-1 and the fungal population less than 8 × 10⁴ CFU mL^-1 or if the direct cell count becomes lower than 50 × 10⁴ cells mL^-1 in bacteria and 8 × 10² cells mL^-1 in fungi.

Conclusion

The biomixture based on banana stem supports the microbial activity necessary for the degradation of the EBDC pesticide. It was found that fungi could be used as indicators of the pollutant degradation process in the biomixtures. Microbial counts were useful to establish the mobility and degradation time of the pesticide and the effectiveness of the biomixture. Based on the results, it is appropriate to include the quantification of microbial populations to assess the effectiveness of pesticide degradation and the maturity level of the biomixture.