The gut microbiota has been increasingly recognized to regulate host fitness, which in turn is dependent on stability of community structure and composition. Many biotic and abiotic factors have been demonstrated to shape gut microbiota of cladocerans. However, the interactive effects of these variables on cladocerans fitness due to alteration of gut microbiota and their linkage with life history parameters are poorly understood. Here, we investigated the responses of Daphnia magna gut microbiota to the combined effects of toxic Microcystis aeruginosa and high temperature and its associations with fitness. We found that under good food regime, the temperature has no effect on the composition of the gut microbiota, whereas under high proportion of toxic M. aeruginosa and high temperature conditions, D. magna lost their symbionts. High proportion of toxic M. aeruginosa and high temperature had synergistically negative effects on D. magna performance due to altered gut microbiota. The high abundance of symbiotic Comamonadaceae and good food increased D. magna fitness. The present study illustrates that understanding life history strategies in response to multiple stressors related to changes in the gut microbiota diversity and composition requires integrated approaches that incorporate multiple linked traits and tether them to one another.

Organosilicons are widely used in consumer products and are ubiquitous in living environments. However, there is little systemic information on this group of pollutants in ambient particles. This study proposes a novel untargeted strategy based mainly on the mass difference of three silicon isotopes to screen organosilicon compounds from 2-year PM₂.₅ samples of Beijing using gas chromatography and high-resolution time-of-flight mass spectrometry. 61 organosilicons were filtered from 1019 peaks, and 35 ones were identified as organosiloxanes including 17 methylsiloxanes and 18 phenylmethylsiloxanes, of which 6 and 3 species were confirmed using reference standards, respectively. These organosiloxanes could be clustered into three groups: low-silicon-number methylsiloxanes, high-silicon-number methylsiloxanes, and phenylmethylsiloxanes. Low-silicon-number methylsiloxanes showed high abundance in the heating season but low abundance in the non-heating season, whereas high-silicon-number methylsiloxanes showed the opposite seasonal variation. This study provides a promising strategy for screening organosilicon compounds through an untargeted approach and gives insights for further investigation of the sources and health risks of organosiloxanes.

In this study, we examined the change rates of PM₂.₅ concentrations, aerosol optical depth (AOD), and the concentrations of PM₂.₅ precursors, such as SO₂ and NO₂, in China and South Korea using surface and satellite observations from 2015 to 2018. To quantify the impacts of the emissions and meteorology on the concentration changes, we performed a series of air quality simulations with year-specific meteorology and a fixed anthropogenic emissions inventory. The surface PM₂.₅ observations in China and South Korea decreased at rates of 9.1 and 4.3%/yr during the study period, respectively. The AODs from Moderate Resolution Imaging Spectroradiometer (MODIS) and Geostationary Ocean Color Imager (GOCI) also decreased faster over China than the AODs over South Korea. For the PM₂.₅ decrease in China, the emission impact was more significant (73%) than the meteorology impact (27%). On the contrary, in South Korea, the emissions and meteorology impacts on PM₂.₅ reductions were similar (51% vs 49%). The SO₂ concentration over China in 2018 significantly reduced to approximately half of the level in 2015. In turn, the sulfate concentration in Baengnyeong (BN), located in a downwind pathway from China to South Korea, decreased at a rate of 0.79%/month. However, the nitrate concentration in BN showed an increasing trend due to the non-linear chemical reactions among sulfate-nitrate-ammonium. The increased nitrate compensated for the reduced PM₂.₅ concentration from the sulfate decrease at BN. Additionally, the number of high (>50 μg/m³) PM₂.₅ concentration days continuously decreased in China, but the number in South Korea increased. It is noted that emission reductions in an upwind area do not guarantee corresponding air quality improvement in the downwind area when complex secondary aerosol formation processes, as well as spatiotemporal changes in meteorology, are involved in the transboundary transport of air pollutants.

The spread of antibiotic resistance genes (ARGs) is a global environmental issue. Dissolved biochar is more likely to contact bacteria in water, producing ecological risks. This study explored the effects of dissolved biochar on ARGs transfer in bacteria. Conjugative transfer efficiency was significantly different following treatment with different types of dissolved biochar. Typically, humic acid-like substance in dissolved biochar can significantly improve the transfer efficiency of ARGs between bacteria. When the concentration of dissolved biochar was ≤10 mg biochar/mL, humic acid-like substance substantially promoted ARGs transfer. An increase in dissolved biochar concentration weakened the ARGs transfer from humic acid-like substance. The inhibitory effects of small-molecule matters dominated, decreasing conjugative transfer frequency. At a concentration of 100 mg biochar/mL, the conjugative transfer efficiency of all treatments was lower than that of control. Compared with corn straw dissolved biochar, there were more transconjugants in pine sawdust dissolved biochar. Following treatment with 10 mg biochar/mL pine sawdust dissolved biochar, the number of transconjugants was at its maximum; approximately 7.3 folds higher than the control. We also explored mechanisms by which dissolved biochar impacts conjugative transfer. Due to the complex composition of dissolved biochar, its effects on the expression of conjugative transfer-related genes were also dynamic. This study investigates the ecological risk of biochar and guides its scientific application.

Current understanding of biochar's effect on antibiotic resistance genes (ARGs) in soil is limited, and whether the effect could change after long-term field aging remains largely unknown. In this study, we employed high-throughput quantitative PCR to assess the effect of biochar amendment on soil resistome as affected by three years of field aging. Application of fresh biochar significantly elevated the number and abundance of ARGs in the manured soil, but did not show such effect under pakchoi cultivation. The presence of aged biochar caused a marked reduction of ARGs only in the planted manured soil. Results of principal coordinate analysis and structural equation modeling indicate that biochar's effect on soil ARG profile was changed by field aging through altering soil microbial composition. These results highlight the necessity of considering aging effect of biochar during its on-farm application to mitigate soil antibiotic resistance.

Both soil microbial nitrate (NO₃⁻-N) immobilization and denitrification are carbon (C)-limited; however, to what extent organic C addition may increase NO₃⁻-N immobilization while stimulate denitrification nitrogen (N) loss remains unclear. Here, ¹⁵N tracing coupled with acetylene inhibition methods were used to assess the effect of adding glucose, wheat straw and peanut straw on NO₃⁻-N immobilization and denitrification under aerobic conditions in an upland soil, in which NO₃⁻-N immobilization has been previously demonstrated to be negligible. The organic C sources (5 g C kg⁻¹ soil) were added in a factorial experiment with 100, 500, and 1000 mg N kg⁻¹ soil (as K¹⁵NO₃) in a 12-d laboratory incubation. Microbial NO₃⁻-N immobilization in the 12-d incubation in the three N treatments was 5.5, 7.7, and 8.2 mg N kg⁻¹ d⁻¹, respectively, in the glucose-amended soil, 5.9, 4.2, and 2.4 mg N kg⁻¹ d⁻¹, respectively, in the wheat straw-amended soil, and 4.9, 5.1 and 4.4 mg N kg⁻¹ d⁻¹, respectively, in the peanut straw-amended soil. Therefore, under sufficient NO₃⁻-N substrate, the higher microbial NO₃⁻-N immobilization in the glucose than in the crop residue treatments was likely due to the slow decomposition of the latter that provided low available C. The ¹⁵N recovery in the N₂O + N₂ pool over the12-day incubation was <2% for all treatments, indicating negligible denitrification N loss due to low denitrification rates in the aerobic incubation in spite of increasing C availability. We conclude that external C addition can enhance microbial NO₃⁻-N immobilization without causing large N losses through denitrification. This has significant implications for reducing soil NO₃⁻-N accumulation by enhancing microbial NO₃⁻-N immobilization through increasing C inputs using organic materials and subsequently mitigating nitrate pollution of water bodies.

Beaches are key attractions for tourism and recreation, and considerable effort is made to keep beaches clean, yet many beaches still have substantial litter loads. Lasting solutions to reduce the amounts of marine litter require an understanding of litter sources. We collected bottles and other single-use containers at 32 sites around the South African coast to infer their sources based on their age and country of manufacture. Bottle densities varied greatly among beaches (8–450 bottles·km⁻¹), depending on proximity to local urban centres and beach cleaning frequency. Most bottles were plastic, despite well-developed recycling initiatives for PET and HDPE bottles in South Africa. Street litter was dominated by bottles made in South Africa (99%), but foreign-manufactured bottles comprised up to 74% of bottles at some beaches, with an increase from urban (4%) through semi-urban (24%) to remote beaches (45%). Most foreign bottles were PET drink bottles from China and other Asian countries, followed by South America and Europe, with little regional variation in the contribution from these sources. This fact, coupled with their recent manufacture dates (mainly <2 years old), indicates that most foreign PET drink bottles are dumped illegally from ships. By comparison, foreign HDPE bottles were more common along the southeast coast of South Africa than along the west coast, consistent with many of these bottles arriving by long-distance drift across the Indian Ocean from southeast Asia. The most common country of origin for these bottles was Indonesia, and most newly-arrived HDPE bottles were 4–6 years old. To tackle beach litter in South Africa we need to greatly reduce plastic leakage from land-based sources, both locally and in southeast Asia, as well as improve measures to prevent the illegal dumping of plastics and other persistent wastes from ships.

Evidence of the effects of long-term household air pollution (HAP) on human mental health is limited. This study aimed to explore the longitudinal relationship between long-term household air pollution exposure from solid fuel use and depression based on nationally representative follow-up dataset. A total of 7005 middle- and old-age adults from the latest four waves (2011, 2013, 2015, and 2018) of China Health and Retirement Longitudinal Study (CHARLS) were involved. The Center for Epidemiologic Studies Depression scale (CES-D 10) was used to measure depressive symptoms and individuals who got more than 12 points were considered to have depression symptoms. We conducted Cox proportional hazards regression models to examine the association between household air pollution and depression in overall population, and subgroup stratified by socio-demographic factors, lifestyle behaviors, chronic diseases, and residential environments. We found long-term household air pollution exposure from solid fuel use was significantly associated with higher depression risk among Chinese older adults (HR 1.27, 95% CI 1.14–1.42 in heating; 1.26, 1.13–1.40 in cooking). Longer duration of household air pollution exposure (1.47, 1.28–1.68 in heating; 1.36, 1.19–1.56 in cooking) and household air pollution from crop residue/wood burning (1.66, 1.41–1.94 in heating; 1.37, 1.23–1.53 in cooking) was correlated with higher depression risk. For subgroups analysis, the effect of household air pollution from solid fuel on depression varied. Compared with those who using clean fuel, older adults living in small size houses or houses with small number rooms had increasing depression risks if they used solid fuel for heating or cooking. Our findings indicate long-term household air pollution exposure from solid fuel use is associated with higher depression risk. Reducing household air pollution by restricting solid fuel use can be effective ways to prevent depression for Chinese older adults and decrease related public health burden.