Detecting microplastics in organic-rich materials and their potential risks to earthworms in agroecosystems.

Microplastics (MPs) are a major emerging contaminant in agroecosystems, due to their significant resistance to degradation in terrestrial environments. Although previous investigations have reported the harmful effects of MPs contamination on soil biological properties, still little is known about the characteristics and fate of MPs in biosolid-amended soils and their risks to soil biota, particularly earthworms. We determined microplastics' concentration, size distribution, and chemical composition in 3 sewage sludge biosolids and 6 biosolid-amended agricultural soils. In addition, we assessed the potential short-term risks of MPs to earthworms' (Amynthas Gracilis and Eisenia Fetida) survival rate and fitness in an environmentally relevant exposure study (28 days). Biosolid-amended soils (1000-3100 MPs kg-1 dry mass) showed ≈30 times lower MPs content than investigated biosolids (55400-73800 MPs kg-1 dry mass), with microplastic fragment to fibre ratios between 0.2 and 0.6 and 0.3-0.4 in soils and biosolids, respectively. Total MPs dry mass was also ≈19 times lower in assessed soils (12-26 mg kg-1) than biosolids (328-440 mg kg-1). On average 77% and 80% of plastic fragments had a lower dimension than 500 µm, while 50% and 67% of plastic fibres had a length of less than 1000 µm in soil and biosolid samples, respectively. Polyethylene (23.6%) was the major source of microplastic contamination in biosolid-amended soils, while polyethylene terephthalate (41.6%) showed the highest concentration in biosolid samples. Spiked polyethylene MPs did not show any significant effect on earthworms' survival rate (93-99%). However, biosolid application significantly (P < 0.05) decreased survival rate of Eisenia Fetida (81%) but showed no significant effect on Amynthas Gracilis (93%). Biosolid amendment significantly (P < 0.05) decreased earthworms' growth rate, with higher impact on Eisenia Fetida than Amynthas Gracilis, while there were no significant differences between control and microplastic spiked treatments. The overall decrease in MPs concentration of earthworm casts, compared with initial MPs concentrations in soil, indicated that the investigated species did not bioaccumulate MPs during the exposure experiment.

Soil organic matter formation is controlled by the chemistry and bioavailability of organic carbon inputs across different land uses.

Soil organic matter (SOM) formation involves microbial transformation of plant materials of various quality with physico-chemical stabilisation via soil aggregation. Land use and vegetation type can affect the litter chemistry and bioavailability of organic carbon (OC), and consequently influence the processing and stabilisation of OC into SOM. We used 13C nuclear magnetic resonance (13C NMR) and hot-water extraction to assess the changes in chemical composition and labile OC fractions during the transformation processes from leaf to litter to SOM depending on land use and vegetation type. The hot-water-extractable OC (HWEOC) decreased from leaf (43-65 g kg-1) to litter (19-23 g kg-1) to SOM (8-16 g kg-1) similar in four land use types: grassland, sugarcane, forest and banana. These trends demonstrated the uniform converging pathways of OC transformation and increasing stability by SOM formation. The preferential decomposition and decrease of labile OC fractions (∑% di-O-alkyl, O-alkyl and methoxyl) from leaf (54-69%) to SOM (41-43%) confirmed the increasing stability of the remaining compounds. Despite differences in the biochemical composition of the leaf tissues among the vegetation types, the proportions of labile OC fractions in SOM were similar across land uses. The OC content of soil was higher in forest (7.9%) and grassland (5.2%) compared to sugarcane (2.3%) and banana (3.0%). Consequently, the HWEOC per unit of soil weight was higher in forest and grassland (2.0 and 1.2 g kg-1 soil, respectively) compared to sugarcane and banana (0.3 and 0.4 g kg soil-1, respectively). The availability of labile SOM is dependent on the quantity of SOM not the chemical composition of SOM. In conclusion, labile OC fractions in SOM, as identified by 13C NMR, were similar across land use regardless of vegetation type and consequently, SOM formation leads to convergence of chemical composition despite diversity of OC sources.

Tracing the sources of sediment and associated particulate nitrogen from different land uses in the Johnstone River catchment, Wet Tropics, north-eastern Australia.

While the ecosystem of the Great Barrier Reef (GBR), north-eastern Australia, is being threatened by the elevated levels of sediments and nutrients discharged from adjacent coastal river systems, the source of these detrimental pollutants are not well understood. Here we used a combined isotopic (δ13C, δ15N) and geochemical (Zn, Pt and S) signatures and stable isotope analysis in R (SIAR) mixing model to estimate the contribution of different land uses to the sediment and associated particulate nitrogen delivered to the Johnstone River. Results showed that rainforest was the largest contributor of suspended and bed sediments in the river estuary (both 33.1%), followed by banana (26.7%, 20.4%), sugarcane (21.5%, 21.4%) and grazing (18.7%, 25.1%). However, bananas and sugarcane land uses had the highest contribution to sediments delivered to the coast per unit of area. This will help land managers to prioritise on-ground activities to improve water quality in the GBR lagoon.

Spatial and temporal dynamics of nutrients in riparian soils after nine years of operation of the Three Gorges Reservoir, China.

The construction and operation of the Three Gorges Reservoir (TGR), the largest hydropower dam in the world, has had significant consequences for the hydrology of riparian zones along the Yangtze river. Little is known about how such changes in hydrology might affect the levels of nutrients and organic matter (OM) in riparian soils. We conducted a nine-year study on the spatio-temporal dynamics and dominant environmental correlates of nutrients and OM in riparian soils along a 600 km section of the Yangtze. These soils have been exposed to a disrupted hydrological regime since the TGR's establishment in 2008. Vegetation surveys were also conducted from 2012 to 2016 to assess relationships between soil chemical properties and vegetation community properties under altered hydrology. Across the stream gradient, concentrations of total potassium (K) increased by 54% since the TGR's establishment. The opposite occurred for SOM and available K, concentrations of which were 35% and 33% lower in 2016, respectively, than those of 2008. The rate of increase in total K tended to be more rapid at the middle section of the stream gradient. Moreover, concentrations of SOM, total N, total K, and available phosphorus (P) and K tended to be particularly high at the middle section. The spatio-temporal distributions of nutrients were strongly positively related to the contents of fine soil particles (i.e., silt and clay). Moreover, the aboveground biomass was negatively correlated with the nutrient dynamics. Our results indicate that the control of the nutrient release in the middle reaches and lower elevations where fine particles tend to accumulate, will be essential for maintaining the health of aquatic and riparian ecosystems upstream of the TGR.

Biochar amendment and water stress alter rhizosphere carbon and nitrogen budgets in bauxite-processing residue sand under rehabilitation.

Nitrogen (N) bioavailability is one of the main limiting factors for microbial activity and vegetation establishment in bauxite-processing residue sand (BRS). Although beneficial effects of biochar on reducing N loss in the early stages of BRS rehabilitation have been observed previously, the underlying mechanisms of this complicated process, particularly the interactions between applied biochar and the plant rhizosphere is largely unknown. This glasshouse study (116 days), investigated the coupled effects of biochar and water stress on N bioavailability in the rhizosphere of ryegrass (Lolium rigidum) grown in BRS amended with di-ammonium phosphate (DAP) fertiliser (at rates of 0 or 2.7 t ha-1) with and without biochar amendment. The applied biochar was characterised as either aged acidic (AC) or alkaline pine (PC) and was mixed with BRS at a rate of 5% v/v under four moisture regimes (50%, 40%, 20% and 7.5% water holding capacity). Amending BRS with AC and PC biochars increased NH4+ retention and decreased cumulative NH3 volatilization within both the rhizosphere and root-free zones compared with fertiliser only treatment. These effects were more pronounced for the AC than PC biochar, suggesting that aged acidic biochar has the great potential for use in rapid establishment of vegetation in BRS disposal areas. The biochar amendment increased cumulative nitrous oxide emissions compared with DAP only treatment, with no significant differences among different moisture regimes. The Control and 20% water holding capacity (WHC) treatment showed the highest dissolved organic carbon (DOC) concentrations compared with other treatments and moisture regimes in the ryegrass rhizosphere, while the highest dissolved organic N concentration were observed in the DAP + AC treatment. Reducing moisture levels below 20% WHC generally decreased microbial biomass carbon (MBC) concentrations and activity in both the rhizosphere and root-free zones of all treatments, while total N generally decreased as moisture levels decreased from 50% to 7.5% WHC. Plant took up more N in the DAP + AC treatment compared with DAP + PC and DAP only treatments, while increasing water stress generally resulted in decreased aboveground biomass.

A novel approach of combining isotopic and geochemical signatures to differentiate the sources of sediments and particulate nutrients from different land uses.

Determining the source of sediments and associated nutrients from terrestrial to aquatic environments is critical for managing the detrimental impacts of soil erosion and loss of nutrients from terrestrial into aquatic environment. However, tracing the source of particulate nutrients from different land uses has not been adequately carried out due to methodological difficulties in separating sources, particularly in the Great Barrier Reef (GBR) catchment. The objective of this study was to develop a method to differentiate the sources of particulate nutrients from soils collected from different land uses (combination of beef and dairy grazing, sugarcane, forest and banana) using both geochemical and isotopic signatures. In order to select a discriminative group of signatures, all soil samples collected from each of the land use areas were fractionated to <63 µm size fraction and were analysed for both isotopic (δ13C, δ15N) and acid extractable geochemical properties (e.g. Zn, Pt and S). Considering the fact that the outcome of tracing models often depends on the type and robustness of the methods used, here we have employed a stable isotope mixing model (SIAR) to evaluate if the suite of selected elements could be used to estimate the relative contribution of different sources for a series of five virtually created sediment mixtures. For the five groups of virtual sediments, the SIAR model provided close estimates to the contribution values of sediment sources with the Mean Absolute Error (MAE) varying from 0.30 to 2.88%. Results from this study show for the first time that the combined use of isotopic and geochemical signatures enable the SIAR model to provide an accurate estimation of source apportionment where a variety of land uses needs to be investigated and shows promise as a valuable new sediment and particulate nutrient tracing tool.

Responses of labile soil organic carbon and nitrogen pools to long-term prescribed burning regimes in a wet sclerophyll forest of southeast Queensland, Australia.

Soil labile organic carbon (C) and nitrogen (N) pools play a central role in nutrient cycling, while fire is a key driver of biogeochemical cycle, shaping ecosystem structure and functioning. However, how soil labile organic C and N responds to the long-term repeated prescribed fire is largely unknown. In this study, a prescribed fire field experiment in a wet sclerophyll forest established in 1972 in southeast Queensland was used to evaluate the long-term impacts of different fire frequency regimes on labile organic C and N measured by different extraction methods. The fire frequency regimes included long unburnt (NB), burnt every two years (2yrB) and burnt every four years (4yrB). Results revealed that the 2yrB treatment had significantly lower C and N concentrations in hot water and K2SO4 extracts and in density fractions (LFD<2.3 and HFD>1.6) compared with the NB treatment. Concentrations of carbohydrate-C in hot water extracts and acid soluble and insoluble organic matter-C in cold-water extracts followed a similar trend. The maximum reduction was observed for carbohydrate­C (72%) and the hot water extractable N (54%) in the 2yrB treatment compared with the NB treatment, showing these parameters are most sensitive indicators. However, there was no significant difference in most of the above parameters between the 4yrB and the NB treatments, indicating that less frequent fire (4yrB) allows the ecosystem to have sufficient time to recover from fire disturbance and may be a sustainable practice for fire management in this wet sclerophyll forest ecosystem.

Role of oxygen-containing functional groups in forest fire-generated and pyrolytic chars for immobilization of copper and nickel.

Char as a carbon-rich material, can be produced under pyrolytic conditions, wildfires or prescribed burn offs for fire management. The objective of this study was to elucidate mechanistic interactions of copper (Cu2+) and nickel (Ni2+) with different chars produced by pyrolysis (green waste, GW; blue-Mallee, BM) and forest fires (fresh-burnt by prescribed fire, FC; aged char produced by wild fire, AC). The pyrolytic chars were more effective sorbents of Cu2+ (∼11 times) and Ni2+ (∼5 times) compared with the forest fire chars. Both cross-polarization (CPMAS-NMR) and Bloch decay (BDMAS-NMR) 13C NMR spectroscopies showed that forest fire chars have higher woody components (aromatic functional groups) and lower polar groups (e.g. O-alkyl C) compared with the pyrolytic chars. The polarity index was greater in the pyrolytic chars (0.99-1.34) than in the fire-generated chars (0.98-1.15), while aromaticity was lower in the former than in the latter. Fourier transform infrared (FTIR) and Raman spectroscopies indicated the binding of carbonate and phosphate with both Cu2+ and Ni2+ in all chars, but with a greater extent in pyrolytic than forest fire-generated chars. These findings have demonstrated the key role of char's oxygen-containing functional groups in determining their sorption capacity for the Cu2+ and Ni2+ in contaminated lands.

Can opium abuse be a risk factor for carotid stenosis in patients who are candidates for coronary artery bypass grafting?

BACKGROUND: Over the centuries, opium has been the most frequent substance abused in the Middle East. There are many controversial aspects about the effects of opioids on the atherosclerosis process, which is still unclear. METHODS: All patients who were candidates for coronary artery bypass graft in Tehran Heart Center were registered and evaluated for risk factors such as diabetes mellitus, hypertension, smoking status and duration, opium abuse, involved coronary arteries and left main branch lesion > 50%, carotid stenosis > or = 70%. RESULTS: A total of 1,339 patients were enrolled in the study, of whom 400 (29.9%) were female and the other 939 (70.1%) male. Female patients were omitted from analysis due to the low numbers of female opium addicts. Our study revealed that in the addicted population, the risk of diabetes and hypertension was lower than in the non-addicted group (p < 0.05 for each variable) and fasting blood sugar tended to be less in addicted ones, but the number of involved coronary arteries, left main stenosis > 50% and extent of carotid stenosis was not significantly different between the two groups. CONCLUSIONS: Our investigations demonstrate that opium is not cardioprotective, as has been claimed by some previous studies, and does not even decelerate atherosclerosis of carotid arteries in opium-addicted patients, but more evidence is still needed to completely prove the case.

Ultrasonographic screening for abdominal aortic aneurysms in Iranian candidates for coronary artery bypass graft surgery.

BACKGROUND: To evaluate the prevalence of abdominal aortic aneurysm in Iranian candidates for coronary artery bypass graft surgery and its associated factors. METHODS: Totally, 2843 consecutive candidates for coronary artery bypass graft surgery underwent ultrasonography of abdominal aorta. The relation between abdominal aortic aneurysm with gender, age, smoking, dyslipidemia, hypertension, diabetes, and carotid and coronary stenosis was evaluated. RESULTS: The prevalence of abdominal aortic aneurysm was 2.7% and 0.7% in men and women subgroups, respectively. The prevalence was 3.8% in men older than 65 years. The largest diameter of abdominal aortic aneurysm was 61.7 mm. Only two men had aneurysm larger than 55 mm, which led to changing their surgery schedule to stenting. Gender, age, smoking, smoking more than 40 years, diabetes , hypertension, and significant carotid stenosis were associated factors of abdominal aortic aneurysm. CONCLUSION: Compared with the results sited in Western studies, the prevalence of abdominal aortic aneurysm is lower in Iran (P<0.0001). Its associated factors in our study were similar to previously published studies. Significant carotid stenosis, a factor not reported previously, was an associated factor in our study. Because of the low prevalence of abdominal aortic aneurysm in our population, screening the candidates for coronary artery bypass graft surgery is not recommended.

Preoperative carotid artery screening in patients undergoing coronary artery bypass graft surgery.

BACKGROUND: The incidence of stroke is 2.1-5.2% in bypass surgery patients with a mortality of 0-38%. This study was designed to evaluate the incidence of significant carotid artery stenosis and its related risk factors in candidates for coronary artery bypass graft (CABG) surgery. METHODS: One thousand forty five consecutive candidates for CABG underwent carotid artery Doppler examination in a prospective study. The relation of age, sex, smoking and diabetes history, as well as lipid profile with carotid stenosis, was evaluated. RESULTS: In 1045 CABG candidates with a mean age of 60 years, prevalence of significant carotid stenosis (>60%) was 6.9%. In the patients aged 65 years and older, the rate of significant stenosis was 12.5%. Age >50 years, female gender, hypercholesterolemia and diabetes mellitus are independent risk factors for significant carotid stenosis. CONCLUSIONS: Significant carotid stenosis has an earlier appearance in our study. Cost-effectiveness studies are recommended for revising the previous screening protocols.