Biochar produced by pyrolysis of biomass can be used to counter nitrogen (N) pollution. The present study investigated the effects of feedstock and temperature on characteristics of biochars and their adsorption ability for ammonium N (NH4+-N) and nitrate N (NO3−-N). Twelve biochars were produced from wheat-straw (W-BC), corn-straw (C-BC) and peanut-shell (P-BC) at pyrolysis temperatures of 400, 500, 600 and 700°C. Biochar physical and chemical properties were determined and the biochars were used for N sorption experiments. The results showed that biochar yield and contents of N, hydrogen and oxygen decreased as pyrolysis temperature increased from 400°C to 700°C, whereas contents of ash, pH and carbon increased with greater pyrolysis temperature. All biochars could sorb substantial amounts of NH4+-N, and the sorption characteristics were well fitted to the Freundlich isotherm model. The ability of biochars to adsorb NH4+-N followed: C-BC>P-BC>W-BC, and the adsorption amount decreased with higher pyrolysis temperature. The ability of C-BC to sorb NH4+-N was the highest because it had the largest cation exchange capacity (CEC) among all biochars (e.g., C-BC400 with a CEC of 38.3 cmol kg−1 adsorbed 2.3 mg NH4+-N g−1 in solutions with 50 mg NH4+ L−1). Compared with NH4+-N, none of NO3−-N was adsorbed to biochars at different NO3− concentrations. Instead, some NO3−-N was even released from the biochar materials. We conclude that biochars can be used under conditions where NH4+-N (or NH3) pollution is a concern, but further research is needed in terms of applying biochars to reduce NO3−-N pollution.

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Effects of feedstock and pyrolysis temperature on biochar adsorption of ammonium and nitrate.

Microplastics in soils: A review of methods, occurrence, fate, transport, ecological and environmental risks.

A review on biochar modulated soil condition improvements and nutrient dynamics concerning crop yields: Pathways to climate change mitigation and global food security.

Plastic pollution is one of the most pressing environmental and social issues of the 21st century. Recent work has highlighted the atmosphere’s role in transporting microplastics to remote locations [S. Allen et al., Nat. Geosci. 12, 339 (2019) and J. Brahney, M. Hallerud, E. Heim, M. Hahnenberger, S. Sukumaran, Science 368, 1257–1260 (2020)]. Here, we use in situ observations of microplastic deposition combined with an atmospheric transport model and optimal estimation techniques to test hypotheses of the most likely sources of atmospheric plastic. Results suggest that atmospheric microplastics in the western United States are primarily derived from secondary re-emission sources including roads (84%), the ocean (11%), and agricultural soil dust (5%). Using our best estimate of plastic sources and modeled transport pathways, most continents were net importers of plastics from the marine environment, underscoring the cumulative role of legacy pollution in the atmospheric burden of plastic. This effort uses high-resolution spatial and temporal deposition data along with several hypothesized emission sources to constrain atmospheric plastic. Akin to global biogeochemical cycles, plastics now spiral around the globe with distinct atmospheric, oceanic, cryospheric, and terrestrial residence times. Though advancements have been made in the manufacture of biodegradable polymers, our data suggest that extant nonbiodegradable polymers will continue to cycle through the earth’s systems. Due to limited observations and understanding of the source processes, there remain large uncertainties in the transport, deposition, and source attribution of microplastics. Thus, we prioritize future research directions for understanding the plastic cycle.

https://www.pnas.org/content/pnas/118/16/e2020719118.full.pdf

Constraining the atmospheric limb of the plastic cycle.

Plastic pollution is ubiquitous in terrestrial and aquatic ecosystems. Plastic waste exposed to the environment creates problems and is of significant concern for all life forms. Plastic production and accumulation in the natural environment are occurring at an unprecedented rate due to indiscriminate use, inadequate recycling, and deposits in landfills. In 2019, the global production of plastic was at 370 million tons, with only 9% of it being recycled, 12% being incinerated, and the remaining left in the environment or landfills. The leakage of plastic wastes into terrestrial and aquatic ecosystems is occurring at an unprecedented rate. The management of plastic waste is a challenging problem for researchers, policymakers, citizens, and other stakeholders. Therefore, here, we summarize the current understanding and concerns of plastics pollution (microplastics or nanoplastics) on natural ecosystems. The overall goal of this review is to provide background assessment on the adverse effects of plastic pollution on natural ecosystems; interlink the management of plastic pollution with sustainable development goals; address the policy initiatives under transdisciplinary approaches through life cycle assessment, circular economy, and sustainability; identify the knowledge gaps; and provide current policy recommendations. Plastic waste management through community involvement and socio-economic inputs in different countries are presented and discussed. Plastic ban policies and public awareness are likely the major mitigation interventions. The need for life cycle assessment and circularity to assess the potential environmental impacts and resources used throughout a plastic product’s life span is emphasized. Innovations are needed to reduce, reuse, recycle, and recover plastics and find eco-friendly replacements for plastics. Empowering and educating communities and citizens to act collectively to minimize plastic pollution and use alternative options for plastics must be promoted and enforced. Plastic pollution is a global concern that must be addressed collectively with the utmost priority.

Impacts of Plastic Pollution on Ecosystem Services, Sustainable Development Goals, and Need to Focus on Circular Economy and Policy Interventions

Plastic pollution is a global concern given its prevalence in aquatic and terrestrial ecosystems. Studies have been conducted on the distribution and impact of plastic pollution in marine ecosystems, but little is known on terrestrial ecosystems. Plastic mulch has been widely used to increase crop yields worldwide, yet the impact of plastic residues in cropland soils to soil health and crop production in the long term remained unclear. In this paper, using a global meta-analysis, we found that the use of plastic mulch can indeed increase crop yields on average by 25%-42% in the immediate season due to the increase of soil temperature (+8%) and moisture (+17%). However, the unabated accumulation of film residues in the field negatively impacts its physicochemical properties linked to healthy soil and threatens food production in the long term. It has multiple negative impacts on plant growth including crop yield (at the mean rate of -3% for every additional 100 kg/ha of film residue), plant height (-2%) and root weight (-5%), and soil properties including soil water evaporation capacity (-2%), soil water infiltration rate (-8%), soil organic matter (-0.8%) and soil available phosphorus (-5%) based on meta-regression. Using a nationwide field survey of China, the largest user of plastic mulch worldwide, we found that plastic residue accumulation in cropland soils has reached 550,800 tonnes, with an estimated 6%-10% reduction in cotton yield in some polluted sites based on current level of plastic residue content. Immediate actions should be taken to ensure the recovery of plastic film mulch and limit further increase in film residue loading to maintain the sustainability of these croplands.

Plastic pollution in croplands threatens long-term food security

This study investigated the effects of maize (Zea mays L.) straw biochar on phosphorus (P) availability in two soils with different P sorption capacities (iron and aluminum dominated slight acid Red earth and calcium dominated alkaline Fluvo-aquic soil). A 42-day incubation experiment was conducted to study how applications of biochar at different rates (0, 2, 4, and 8 % soil, w/w), in combination with and without mineral KH2PO4 fertilizer, affected contents of soil Olsen-P and soil microbial biomass P (SMB-P) and phosphomonoesterase activity. In addition, P sorption characteristics of soils amended with biochar, as well as main properties of the biochar and the soils, were determined. Application of 8 % biochar after 42 days of incubation substantially increased soil Olsen-P from 3 to 46 mg kg−1 in Red earth and from 13 to 137 mg kg−1 in Fluvo-aquic soil and increased SMB-P from 1 to 9 mg kg−1 in Red earth and from 9 to 21 mg kg−1 in Fluvo-aquic soil. The increase was mainly due to high concentrations of P in the ash fraction (77 % of total biochar P). Biochar effect on soil Olsen-P and SMB-P increased by higher biochar application rates and by lower P sorption capacity. Biochar application significantly reduced acid phosphomonoesterase activity in Red earth and alkaline phosphomonoesterase activity in Fluvo-aquic soil due to large amount of inorganic P added. We conclude that maize straw biochar is promising to potentially improve soil P availability in low-P soils, but further research at field scale is needed to confirm this.

Short-term effects of maize residue biochar on phosphorus availability in two soils with different phosphorus sorption capacities

Risks of phosphorus runoff losses from five Chinese paddy soils under conventional management practices

The invention discloses an underground leaching in-situ collection device with a plastic boundary. The underground leaching in-situ collection device comprises a leaching collection body and a leaching solution filtering and collection barrel, wherein the leaching collection body is a cylinder with an opening in the top and is formed by enclosing a waterproof soft thin film; an opening end of the leaching solution filtering and collection barrel is matched with a barrel cover and the barrel cover is in an inward concave form; the barrel cover is provided with a plurality of water filtering holes; the leaching solution filtering and collection barrel is arranged on the lower part of the leaching collection body and is connected with the bottom of the leaching collection body; the bottom of the leaching collection body connected with the leaching solution filtering and collection barrel is provided with through holes corresponding to the water filtering holes; the leaching solution filtering and collection barrel is internally provided with a liquid pumping pipe and an air ventilating pipe; the liquid pumping pipe extends to the upper part of the leaching collection body from the bottom of the leaching solution filtering and collection barrel; the air ventilating pipe extends to the upper part of the leaching collection body from the top of the leaching solution filtering and collection barrel. According to the underground leaching in-situ collection device, the elastic waterproof soft thin film is used as the leaching collection body, so that the pool wall effect caused by expansion with heat and contraction with cold can be effectively overcome.

Bin Xi

Papers

Plastic pollution in croplands threatens long-term food security

Short-term effects of maize residue biochar on phosphorus availability in two soils with different phosphorus sorption capacities

Risks of phosphorus runoff losses from five Chinese paddy soils under conventional management practices

Underground leaching in-situ collection device with plastic boundary