Sewage sludge application as a vehicle for microplastics in eastern Spanish agricultural soils

Sewage sludges applied to agricultural soils are sources of microplastic pollution, however, little is known about the accumulation, persistence, or degradation of these microplastics over time. This is the first study to provide long-term, high temporal resolution quantitative evidence of microplastics in agricultural soils following sewage sludge application. The abundance and degradation of microplastics was assessed in soils sampled biennially from an experimental field over a 25-year period managed under an improved grassland regime following the application of five different sewage sludges. The sludges contained different microplastic compositions reflecting the different sources of the sludges. Microplastic abundance increased by 723-1445% following sewage sludge applications (p<0.05) and remained constant over time (22 years and possibly beyond) (p>0.05). All sludges predominantly added white/transparent microfibres to soil. Microfilms, microfibres, and fragments were most susceptible to degradation, potentially creating micro(nano)plastics. Of note was the discoloration of coloured microfibres, which may be environmentally hazardous due to the toxicity of textile dyes in soil ecosystems. We also found that plastic composition could be used to trace its source. This evidence is useful in informing regulation on sewage sludge use and management, and in assessing the fate and impact of microplastics in soil.

Risk Assessment of Contaminants in Sewage Sludge Applied on Norwegian Soils

Microplastics in agricultural soils in China: Sources, impacts and solutions

Background, Aim and Scope The cow-calf (Bos taurus) industry in subtropical United States and other parts of the world depends almost totally on grazed pastures. Establishment of complete, uniform stand of bahiagrass (BG) in a short time period is important economically. Failure to obtain a good BG stand early means increased encroachment of weeds and the loss of not only the initial investment costs, but production and its cash value. Forage production often requires significant inputs of lime, N fertilizer, and less frequently of P and K fertilizers. Domestic sewage sludge or biosolids, composted urban plant debris, waste lime, phosphogypsum, and dredged materials are examples of materials that can be used for fertilizing and liming pastures. Perennial grass can be a good choice for repeated applications of sewage sludge. Although sewage sludge supply some essential plant nutrients and provide soil property-enhancing organic matter, land-application programs still generate some concerns because of possible health and environmental risks involved. The objectives of this study were to evaluate the cumulative and residual effects of repeated applications of sewage sludge on (i) bahiagrass (BG, Paspalum notatum Flugge) production over years with (1997–2000) and without (2001–2002) sewage sludge applications during a 5-yr period, and (ii) on nutrients status of soil that received annual application of sewage sludge from 1997 to 2000 compared with test values of soils in 2002 (with no sewage sludge application) in South Florida.

Microplastics in wastewater treatment plants and their contributions to surface water and farmland pollution in China

Effects of irrigation on the fate of microplastics in typical agricultural soil and freshwater environments in the upper irrigation area of the Yellow River

The enhancing effect of aerobic thermophilic (AT) bacteria on the production of biogas from anaerobically digested sewage sludge (methanogenic sludge) was investigated. Sewage sludge (5%, w/w) was incubated at 65°C with shaking for a few months to prepare the AT seed sludge. AT sludge was prepared by incubation of the AT seed sludge (5%, v/v) and sewage sludge (5%, w/w) at 65°C with shaking. The addition of this AT sludge (1.2% ± 0.5% of total volatile solids) to methanogenic sludge enhanced the production of biogas. The optimum volume of the addition and the pretreatment temperature of the AT sludge for optimum biogas production were 5% (v/v) and 65°C. Batch-fed anaerobic digestion was covered with the addition of various AT sludges. The AT sludge prepared with the AT seed sludge improved the biogas production by 2.2 times relative to that from the sewage sludge addition. The addition of sludge without AT seed sludge weakly enhanced biogas production. An aerobic thermophilic bacterium (strain AT1) was isolated from the AT seed sludge. Strain AT1 grew well in a synthetic medium. The production of biogas from the anaerobic digestion of sewage sludge was improved by the addition of 5% (v/v) AT1 bacterial culture compared with that from the sewage sludge addition. The addition of AT1 culture reduced the volatile solids by 21%, which was higher than the 12.6% achieved with the sewage sludge addition. The AT1 bacterial culture enhanced the biogas production more than the AT seed sludge. The phylogenetic analysis of the 16 S rRNA gene revealed that strain AT1 is closely related to Geobacillus thermodenitrificans (100% sequence similarity). The improvement in the production of biogas with the AT sludge could be caused by thermophilic bacterial activity in the AT sludge.

Sewage sludge can be used as an expanding agent in the production of lightweight expanded clay aggregate (LECA) mass. The addition of sewage sludge increases the total porosity and decreases the bulk density of a sinter. The addition of sewage sludge to a raw material used in the production of LECA enabled a decrease in the burning temperature for the maintained operational parameters of a lightweight aggregate. The optimum content of sewage sludge added to a raw material used in LECA production was 5% to 15% of dry mass. The addition of sewage sludge in an amount of 5% and 10% caused an increase in closed porosity.

Leaching of heavy metals (Cu, Ni and Zn) and organic matter after sewage sludge application to Mediterranean forest soils

Sewage sludge application alters the composition and co-occurrence pattern of the soil bacterial community in southern China forestlands

Dynamics of phosphatase activities in a cork oak litter ( Quercus suber L.) following sewage sludge application

Organic wastes such as sewage sludge and compost increase the input of carbon and nutrients to the soil. However, sewage sludge-applied heavy metals, and organic pollutants adversely affect soil biochemical properties. Therefore, an incubation experiment lasting 90 days was carried out to evaluate the effect of the addition of two sources of organic C: sewage sludge or composted turf and plant residues to a calcareous soil at three rates (15, 45, and 90 t of dry matter ha−1) on pH, EC, dissolved organic C, humic substances C, organic matter mineralization, microbial biomass C, and metabolic quotient. The mobile fraction of heavy metals (Zn, Cd, Cu, Ni, and Pb) extracted by NH4NO3 was also investigated.The addition of sewage sludge decreased soil pH and increased soil salinity to a greater extent than the addition of compost. Both sewage sludge and compost increased significantly the values of the cumulative C mineralized, dissolved organic C, humic and fulvic acid C, microbial biomass C, and metabolic quotient (qCO2), especially with increasing application rate. Compared to compost, the addition of sewage sludge caused higher increases in the values of these parameters. The values of dissolved organic C, fulvic acid C, microbial biomass C, metabolic quotient, and C/N ratio tended to decrease with time. The soil treated with sewage sludge showed a significant increase in the mobile fractions of Zn, Cd, Cu, and Ni and a significant decrease in the mobile fraction of Pb compared to control. The high application rate of compost resulted in the lowest mobility of Cu, Ni, and Pb. The results suggest that biochemical properties of calcareous soil can be enhanced by both organic wastes. But, the high salinity and extractability of heavy metals, due to the addition of sewage sludge, may limit the application of sewage sludge.

Microplastic pollution in agricultural sites has gained increased attention in recent years. Many studies focused on the impact of plastic residues on soil functions, such as soil physiochemical properties, fertility, and biodiversity. However, research on the transport behavior of microplastics (MPs) in agricultural soil remains rare. Therefore, it is important to understand the transport mechanism of MPs in the natural environment. Plot experiments (1x1 m) were conducted in an agricultural site (silty loam) near Prague to investigate the size-dependent movement of MPs under both artificial irrigation (first campaign) and natural rainfall (second campaign). Before irrigation, fluorescent PE microspheres with four different size ranges (53-63 &amp;#181;m, 125-150 &amp;#181;m, 250-300 &amp;#181;m, 425-500 &amp;#181;m) were mixed with soil and then uniformly distributed on the plot surface (upper 1 cm). Deuterium as a conservative tracer was added and well mixed with water for the rainfall simulation. The rainfall simulation with an intensity of 60 mm/h was applied. Results from the first campaign show that the maximum migration depth of MPs was up to 4-6 cm, which is consistent with the results from the tracer experiment. Moreover, larger particles were mostly found on the top layer up to 2 cm, with small MPs at 53-63 &amp;#181;m transported down to 6 cm. These results indicate that the infiltration of water could enhance the movement of MPs in the soil profile, with smaller MPs having higher mobility under rainfall simulation. This finding provides insight into the mobility of MPs in agricultural soils, and it could be applied for control and risk assessment to estimate the potential of MPs leaching into aquifer systems.

Microplastics are emerging persistent pollutants which have attracted increasing attention worldwide. Although microplastics have been widely detected in aquatic environments, their presence in soil ecosystems remains largely unexplored. Plastic debris accumulates in farmland, causing serious environmental problems, which may directly affect food substances or indirectly affect the members in each trophic level of the food chain. This review summarizes the origins, migration, and fate of microplastics in agricultural soils and discusses the interaction between microplastics and the components in farmland from the perspectives of toxicology and accumulation and deduces impacts on ecosystems by linking the organismal response to an ecological role. The effects on farmland ecosystem function are also discussed, emphasizing the supply of agricultural products, food chain pathways, carbon deposition, and nitrogen cycling and soil and water conservation, as microplastic pollution will affect agricultural ecosystems for a long period, posing an ecological risk. Finally, several directions for future research are proposed, which is important for reducing the effect of microplastics in agricultural systems.

The Philippines is primarily an agricultural country in which most Filipinos depend on the health of the soil for livelihood. Plastic pollution adversely affects agriculture by degrading soil quality, fertility, and crop growth. However, the prevalence of plastic particles such as mesoplastics (>5 mm to 25 mm) and microplastics (<5 mm) in agricultural soils in the Philippines remains poorly understood. This study investigated the prevalence of mesoplastics and microplastics in agricultural soils in Iligan City, Philippines. We collected soil samples from the six sampling stations in high-elevation and low-elevation sites. Mesoplastics and microplastics were examined through manual sorting, categorized based on color, shape, and size, and identified using Fourier-transform infrared spectroscopy (FTIR). Mesoplastics were found to be more prevalent, averaging 2.22 items/kg compared to microplastics 0.83 items/kg. Mesoplastics were mainly white-colored (42%), mostly fragmented (55%), 5–10 mm in size (55%), and were predominantly polypropylene (85%). Microplastics were mainly transparent (40%), composed of fragments and film shapes(46%), and 3–4 mm (93%) in size. Polyethylene was the abundant microplastic polymer type (47%). It was observed that the low-elevation sites had a higher abundance of plastic particles, stressing the need to address local factors in tackling plastic pollution.