Aerobic Water Research Articles

Distribution of methane in the upper water layer of the northern Black Sea: Seasonal and daily trends and seawater-air emissions

We report on methane (CH4) concentration measurements in the northern Black Sea area conducted during 6 cruises with R/V Professor Vodyanitsky from 2017 to 2019. Our work is a multi-season study at a uniform station grid covering an area of 88 × 103 km2 and including three latitudinal transects that comprises both surface and vertical profile water-column measurements. The main goal of the work was to assess the seasonal patterns of vertical CH4 structure in the aerobic water column (upper 100 m) and its emission to the atmosphere.In surface waters, the mean dissolved CH4 concentration ranged from 2.6 nmol L−1 detected in November 2018 to 11.5 nmol L−1 measured in June–July 2018, respectively. Calculated CH4 seawater-air fluxes and saturations were mostly positive (i.e. net flux to atmosphere), and winter fluxes (2.6 μmol m−2 d−1) were higher than summer fluxes (1.6 μmol m−2 d−1) due to the higher wind speed. The integral CH4 flux from the whole study area (88 × 103 km2) ranged from 84 to 235 kM day−1.It was shown that, on average, the methane concentration in the upper layer for deep-water stations where the seabed is located at depths >160 m (σt >16.2) was lower compared to stations at shallow water depths (28–140 m, σt <16.2). The most distinct difference was obtained for the summer season (June–July 2018) and a less significant difference – for spring (April–May 2019) and winter season (November–December 2018). During these seasons the water column was also considerably less saturated in CH4 compared to the entire monitoring period. We observed subsurface maxima, which were generally located at the base of the thermocline and exceeded 100 nmol L−1 at some stations. Exceptions were observed in October 2019 (cruise 110), when vertical CH4 distributions were characterized by two-peaks at ∼20 and ∼50 m depth. The strong influence of the thermohaline structure on the water column CH4 distribution has also been shown in studies of daily dynamics of CH4 vertical profiles in the shallow water region. Despite the high variability of CH4 concentrations, significant similarities in vertical distributions of CH4 and chlorophyll-a for which sub-surface maxima coincided at some stations, are shown. Extremely high concentrations of CH4 (up to 351 nmol L−1) in the near-bottom water layer were revealed during all seasons at the station near the Dnieper paleo-channel at the northwestern edge of the study area. This enrichment is assumed to be caused by methane emissions from gas seeps densely located in this region.

Effects of 17β-Estradiol Pollution on Microbial Communities and Methane Emissions in Aerobic Water Bodies.

17β-Estradiol (E2) is a widely present trace pollutant in aquatic environments. However, its impact on microbial communities in aerobic lake waters, which are crucial for methane (CH4) production, remains unclear. This study conducted an E2 contamination experiment by constructing laboratory-simulated aerobic microecosystems. Using 16S rRNA high-throughput sequencing, the effects of E2 on bacterial and archaeal communities were systematically examined. Combined with gas chromatography, the patterns and mechanisms of E2's impact on CH4 emissions in aerobic aquatic systems were uncovered for the first time. Generally, E2 contamination increased the randomness of bacterial and archaeal community assemblies and weakened microbial interactions. Furthermore, changes occurred in the composition and ecological functions of bacterial and archaeal communities under E2 pollution. Specifically, two days after exposure to E2, the relative abundance of Proteobacteria in the low-concentration (L) and high-concentration (H) groups decreased by 6.99% and 4.01%, respectively, compared to the control group (C). Conversely, the relative abundance of Planctomycetota was 1.81% and 1.60% higher in the L and H groups, respectively. E2 contamination led to an increase in the relative abundance of the methanogenesis functional group and a decrease in that of the methanotrophy functional group. These changes led to an increase in CH4 emissions. This study comprehensively investigated the ecotoxicological effects of E2 pollution on microbial communities in aerobic water bodies and filled the knowledge gap regarding aerobic methane production under E2 contamination.

An innovative fast-start aerobic anode microbial fuel cell biosensor for copper ion detection

The potential of microbial fuel cells (MFCs) based biosensors for water monitoring and early warning is widely recognized. However, the electrochemically active biofilms (EABs) are typically obtained under anaerobic conditions and the formation requires a lengthy time span, which critically limits the application and advancement of the MFCs based monitoring technology. To accelerate the formation rate of EABs and thus shorten the establishment time of MFCs to better meet the needs for early warning and detection of pollutants in the actual aerobic water environment, the aerobic sludge was employed as an inoculation source to construct the MFCs sensing system in this study. It was revealed that biofilms with stable electrochemical properties could be promptly formed within 35 h, reaching a level far ahead of previous studies. Moreover, toxicity tests for copper (Cu2+) ions at concentrations of 1 mg/L, 10 mg/L, and 50 mg/L demonstrated outstanding performance with the maximum inhibition rates of 19.99%, 46.65%, and 53.02% respectively. Remarkably, the response time was found to decrease significantly with the increase of copper ion concentrations. Our results thus open up a new avenue for achieving rapid start-up of MFCs in aerobic conditions, which facilitates the applicability of MFCs based biosensing technology.

Microbial methanogenesis in aerobic water: A key driver of surface methane enrichment in a deep reservoir

Significant amounts of the greenhouse gas methane (CH4) are released into the atmosphere worldwide via freshwater sources. The surface methane maximum (SMM), where methane is supersaturated in surface water, has been observed in aquatic systems and contributes significantly to emissions. However, little is known about the temporal and spatial variability of SMM or the mechanisms underlying its development in artificial reservoirs. Here, the community composition of methanogens as major methane producers in the water column and the mcrA gene was investigated, and the cause of surface methane supersaturation was analyzed. In accordance with the findings, elevated methane concentration of SMM in the transition zone, with an annually methane emission flux 2.47 times higher than the reservoir average on a large and deep reservoir. In the transition zone, methanogens with mcrA gene abundances ranging from 0.5 × 103–1.45 × 104 copies/L were found. Methanobacterium, Methanoseata and Methanosarcina were the three dominate methanogens, using both acetic acid and H2/CO2 pathways. In summary, this study contributes to our comprehension of CH4 fluxes and their role in the atmospheric methane budget. Moreover, it offers biological proof of methane generation, which could aid in understanding the role of microbial methanogenesis in aerobic water.

Enhancement of arsenic uptake and accumulation in green microalga Chlamydomonas reinhardtii through heterologous expression of the phosphate transporter DsPht1

Arsenate (AsV) is a predominant arsenic contaminant in aerobic water. Microalgae have been recently used in the phytoremediation of arsenic-contaminated water. However, the amount of AsV uptake in microalgae is limited, which hinders the application of microalgae in arsenic-contaminated water treatment. Here, we found that the expression of a novel phosphate transporter DsPht1 in Dunaliella salina was highly upregulated after AsV exposure. Fluorescent protein-tagging analysis showed the plasma membrane location of DsPht1. Furthermore, DsPht1 was overexpressed in a model microalga Chlamydomonas reinhardtii. The DsPht1 transgenetic lines accumulated up to 6.4-fold higher total arsenic than the untransformed line, and the AsV amount in total arsenic increased by 8.3-fold. Moreover, the organoarsenic content was also higher in the transgenetic lines. Overall, the DsPht1 transformants generated in this study increased arsenate uptake and transformation, which are promising for the effective phytoremediation of arsenic-contaminated water.

Improved closed test setup for biodegradation testing of slightly volatile substances in water-sediment systems (OECD 308)

Standardized biodegradation testing methods, like the OECD 308 Aerobic and Anaerobic Transformation in Aquatic Sediment Systems, generate data on biodegradation required during environmental risk and hazard assessment of chemicals under different European and international regulations. However, difficulties arise when applying the OECD 308 guideline for testing hydrophobic volatile chemicals. Especially the use of a co-solvent (like acetone) as a measure to facilitate the application of the test chemical in combination with a closed setup to reduce losses due to volatilization tend to deplete/restrict the amount of oxygen in the test system. The result is a low oxygen or even anoxic water column in the water-sediment system. Thus, the degradation half-lives of the chemical generated from such tests are not directly comparable to the regulatory half-life values for Persistence assessment of the test chemical. The aim of this work was to further develop the closed setup to improve and maintain aerobic conditions in the water phase of the water-sediment systems for testing slightly volatile hydrophobic test chemicals. This improvement was attained by optimizing the test system geometry and agitation technique to maintain aerobic conditions in the water phase in a closed test setup, investigating appropriate co-solvent application strategy, and trialing the resulting test setup. This study shows that when using a closed test setup for OECD 308 tests, agitation of the water phase overlaying the sediment and the test item application using low co-solvent volume is critical for maintaining an aerobic water layer.

Protection mechanism of N,N-dimethylformamide on stability of few-layer black phosphorus

Few-layer black phosphorus (LBP) has been widely investigated for its unique optical and electronic properties. As degradation of LBP in ambient conditions largely limited its practical applications, numerous stabilization methods were developed. Understanding stabilization mechanism is essential to development of new protection technologies for LBP. Herein, protection mechanism of the most wildly used exfoliation solvent N,N-dimethylformamide (DMF) on LBP was investigated. DMF was found to accelerate color fading of LBP in aerobic water solution. Nevertheless, dissolvable phosphorus generated from degradation of LBP in the presence of DMF accounted for only 52%–57% of that generated in the absence of DMF. By measuring kinetics constants and activation energies of the degradation reactions, the protection mechanism of DMF was attributed to impede hydrolysis of phosphorus oxides. This was caused by occupation of oxidation sites on LBP by DMF through electrostatic interaction. Insoluble phosphorus oxides in addition to dissolvable phosphorus were observed in DMF exfoliated LBP aqueous solution, providing further evidence for hydrolysis impeding mechanism. This finding threw mechanism light on protection effects of DMF on LBP, providing new knowledge for development of effective stabilization technologies of LBP.

Pathways of methane removal in the sediment and water column of a seasonally anoxic eutrophic marine basin

Methane (CH4) is a key greenhouse gas. Coastal areas account for a major proportion of marine CH4 emissions. Eutrophication and associated bottom water hypoxia enhance CH4 production in coastal sediments. Here, we assess the fate of CH4 produced in sediments at a site in a seasonally anoxic eutrophic coastal marine basin (Scharendijke, Lake Grevelingen, the Netherlands) in spring (March) and late summer (September) in 2020. Removal of CH4 in the sediment through anaerobic oxidation with sulfate (SO42-) is known to be incomplete in this system, as confirmed here by only slightly higher values of δ13C-CH4 and δD-CH4 in the porewater in the shallow sulfate-methane-transition zone (~5-15 cm sediment depth) when compared to deeper sediment layers. In March 2020, when the water column was fully oxygenated, CH4 that escaped from the sediment was at least partially removed in the bottom water through aerobic oxidation. In September 2020, when the water column was anoxic below ~35 m water depth, CH4 accumulated to high concentrations (up to 73 µmol L-1) in the waters below the oxycline. The sharp counter gradient in oxygen and CH4 concentrations at ~35 m depth and increase in δ13C-CH4 and δD-CH4 above the oxycline indicate mostly aerobic water column removal of CH4. Water column profiles of particulate and dissolved Fe and Mn suggest redox cycling of both metals at the oxycline, pointing towards a potential role of metal oxides in CH4 removal. Water column profiles of NH4+ and NO3- indicate removal of both solutes near the oxycline. Analyses of 16S rRNA gene sequences retrieved from the water column reveal the presence of aerobic CH4 oxidizing bacteria (Methylomonadaceae) and anaerobic methanotrophic archaea (Methanoperedenaceae), with the latter potentially capable of NO3- and/or metal-oxide dependent CH4 oxidation, near the oxycline. Overall, our results indicate sediment and water column removal of CH4 through a combination of aerobic and anaerobic pathways, which vary seasonally. Some of the CH4 appears to escape from the surface waters to the atmosphere, however. We conclude that eutrophication may make coastal waters a more important source of CH4 to the atmosphere than commonly assumed.

Effect of groundwater residence time on geogenic fluoride release into groundwater in the Mt. Meru slope area, Tanzania, the Great Rift Valley, East Africa

People living in the Great Rift Valley in East Africa suffer from fluorosis resulting from their consumption of groundwater. This paper shows that geogenic fluoride contamination in a natural water system has changed in the last two decades in the Mt. Meru slope area of northern Tanzania based on water quality, dating of the residence time, and stable isotopes of groundwater. The results demonstrate that 1) the average recharge altitude of groundwater with a high geogenic fluoride concentration is estimated to range from 1900 m to 3000 m on the southern slope of Mt. Meru, and the fluoride concentration tends to increase with an increase in the recharge altitude, 2) the fluoride concentration increases with increasing groundwater residence time for groundwater with a residence time of 20 years or longer, suggesting that water-rock interaction processes (weathering, dissolution, and ion exchange), which depend on the contact time between the volcanic aquifer and groundwater, have predominated for approximately 20 years or longer, and 3) the mixing of aerobic young water and old groundwater has been active for approximately 20 years, and the fluoride concentration is increasing in some shallower well waters. The mixing of fluoride-contaminated groundwater with aerobic water infiltrating the aquifer through pumping groundwater in the last two decades may increase the spread of groundwater contaminated with fluoride due to increased water demand caused by rapid population growth, and urbanization, industrial growth, and the expansion of irrigated agriculture.

Dredge-material created coastal marshes are more effective at improving water quality than natural marshes in early-stage development

Coastal regions around the globe are experiencing land loss due to rising sea level. Some of the largest rates can be found in deltaic Louisiana, USA. Beneficial reuse of dredged sediments to create coastal marshes is one major effort in helping to reverse this land loss. In 2014, the Lake Hermitage Marsh Creation Project created 29 ha of marsh by dredging sand from the bed of the lower Mississippi River. The goal of this study was to determine the ability of these newly created mineral soil marshes to improve water quality. The natural marsh had 8.2 times greater organic matter content than the created marsh, on average. Under aerobic water column conditions, the mean denitrification rate of the natural marsh was 24.5 ± 3.53 mg NO3-N m2 d−1 while the mean denitrification rate of the two created marshes was significantly greater at 63.19 ± 3.44 mg NO3-N m2 d−1. This difference in rates is a result of internal N loading from the highly organic natural marsh soil, which had 3.7 times more extractable ammonium than the created marsh. As organic matter increases in the created marsh soil, the N removal efficiency may decline over time. This difference in efficiency has important implications not only for coastal restoration projects but also for created wetlands, which accrete significant organic matter over time and may lead to reduced efficiency of N removal, driven by internal N loading from soil.

Nano- and micro-scale zerovalent iron-activated peroxydisulfate for methyl phenyl sulfoxide probe transformation in aerobic water: Quantifying the relative roles of SO4·−, Fe(IV), and ·OH

Multiple reactive intermediates have been proposed to be involved in peroxydisulfate (PDS) activation by zerovalent iron (ZVI), including sulfate radical (SO4·−) produced via iron-oxide shell mediated electron transfer, ferryl ion species (Fe(IV)) formed from Fe(II)-PDS interaction, and hydroxyl radical (·OH) generated by ZVI aerobic oxygenation. In this study, evolution of the relative role of these intermediates in microscale and nanoscale ZVI (mZVI vs. nZVI) activated PDS processes is comparatively investigated by using a methyl phenyl sulfoxide (PMSO) probe that selectively reacts with Fe(IV) to produce methyl phenyl sulfone (PMSO2). Interestingly, during PMSO transformation by mZVI/PDS process, yields of PMSO2 (η(PMSO2)) exhibit three-stage behavior that they first increase to a maximum (∼80% but lower than 100%) (Stage I) and then plateau for a period (Stage II) followed by a decrease phase (Stage III). Accordingly, the relative role of Fe(IV) in PMSO transformation is unceasingly improved in Stage I and subsequently reaches equilibrium with that of free radicals in Stage II, while it finally decreases in Stage III. Similar η(PMSO2) evolution trends are obtained in nZVI/PDS process, except that the η(PMSO2) increase in Stage I is negligible, possibly due to the exceptional fast nZVI dissolution. It was further clarified by tert-butyl alcohol scavenging assay that, in addition to Fe(IV), the free radical involved in Stages I and II is SO4·−, while ·OH was dominant in Stage III. Moreover, studies on O2 effect reveal that ZVI aerobic oxygenation participates in mZVI corrosion during the entire process, while it is only involved in nZVI corrosion when PDS content is reduced to a low concentration, indicating that the reactivities of PDS and O2 are similar in mZVI corrosion, but differ greatly in nZVI corrosion. Additionally, effects of reactant dose and pH on η(PMSO2) evolution are also explored. Dynamics of the relative role of different reactive oxidants should be taken into account in further applications of ZVI/PDS in situ chemical remediation technology considering their different chemistries.

Empirical Setting of the Water Stressed Baseline Increases the Uncertainty of the Crop Water Stress Index in a Humid Temperate Climate in Different Water Regimes

Water productivity of rice is imperative for global water security. Currently, water saving management techniques have been proposed and applied to rice systems. The crop water stress index (CWSI) is a major index for evaluating crop water use. The utility of the CWSI in rice in a humid temperate climate has been given little attention. Previous studies have focused on upland crops and readily available constant reference baselines, primarily the water stressed baseline (WSB), which does not inherently reflect transpiration flux. This study examined the performance of the estimated non-water stressed baseline (NWSB) and WSB for rice in a humid climate and the CWSI sensitivity under variable reference baseline scenarios in a 2-year pot trial under phytotron and field environment conditions with two rice genotypes (IRAT109 and Takanari) in a flooded (FL) and aerobic (AR) water regime. We observed that the dynamics of CWSI is dependent not only on the water regimes but could be strongly influenced by genotype sensitivity to vapor pressure deficit (VPD). A higher slope (pooled data) in the field environment (−5.68 °C kPa−1) compared to the phytotron (−3.04 °C kPa−1) reflected transpiration water loss sensitivity to VPD thresholds. Further studies with diverse rice germplasms to explore generalizability to field conditions and reformulation of reference baselines considering the VPD threshold sensitivity could prove to be significant.

NirS-type denitrifying bacteria in aerobic water layers of two drinking water reservoirs: Insights into the abundance, community diversity and co-existence model

The nirS-type denitrifying bacterial community is the main drivers of the nitrogen loss process in drinking water reservoir ecosystems. The temporal patterns in nirS gene abundance and nirS-type denitrifying bacterial community harbored in aerobic water layers of drinking water reservoirs have not been studied well. In this study, quantitative polymerase chain reaction (qPCR) and Illumina Miseq sequencing were employed to explore the nirS gene abundance and denitrifying bacterial community structure in two drinking water reservoirs. The overall results showed that the water quality parameters in two reservoirs had obvious differences. The qPCR results suggested that nirS gene abundance ranged from (2.61 ± 0.12) × 105 to (3.68 ± 0.16) × 105 copies/mL and (3.01 ± 0.12) × 105 to (5.36 ± 0.31) × 105 copies/mL in Jinpen and Lijiahe reservoirs, respectively. The sequencing results revealed that Paracoccus sp., Azoarcus sp., Dechloromonas sp. and Thauera sp. were the dominant genera observed. At species level, Cupriavidus necator, Dechloromonas sp. R-28400, Paracoccus denitrificans and Pseudomonas stutzeri accounted for more proportions in two reservoirs. More importantly, the co-occurrence network analysis demonstrated that Paracoccus sp. R-24615 and Staphylococcus sp. N23 were the keystone species observed in Jinpen and Lijiahe reservoirs, respectively. Redundancy analysis indicated that water quality (particularly turbidity, water temperature, pH and Chlorophyll a) and sampling time had significant influence on the nirS-type denitrifying bacterial community in both reservoirs. These results will shed new lights on exploring the dynamics of nirS-type denitrifying bacteria in aerobic water layers of drinking water reservoirs.

Aerobic and Anaerobic Sea Water Biodegradation Evaluation by Modified Oxygen (O2) Consumption and Gas Pressure Measurement Technique for Synthetic Gas to Liquid (Gtl), Low Aromatic Synthetic Fluids [Lasf] and Synthetic Ethyl Esters of Plants Oils (Seep Mixture) Drilling Fluids in Deep Water Offshore Environment: Process Variables and Optimization

Aerobic and Anaerobic Sea Water Biodegradation Evaluation by Modified Oxygen (O2) Consumption and Gas Pressure Measurement Technique for Synthetic Gas to Liquid (Gtl), Low Aromatic Synthetic Fluids [Lasf] and Synthetic Ethyl Esters of Plants Oils (Seep Mixture) Drilling Fluids in Deep Water Offshore Environment: Process Variables and Optimization

Aerobic and Anaerobic Sea Water Biodegradation Evaluation by Modified Oxygen (O2) Consumption and Gas Pressure Measurement Technique for Synthetic Gas to Liquid (Gtl), Low Aromatic Synthetic Fluids [Lasf] and Synthetic Ethyl Esters of Plants Oils (Seep Mixture) Drilling Fluids in Deep Water Offshore Environment: Process Variables and Optimization

Aerobic and Anaerobic Sea Water Biodegradation Evaluation by Modified Oxygen (O2) Consumption and Gas Pressure Measurement Technique for Synthetic Gas to Liquid (Gtl), Low Aromatic Synthetic Fluids [Lasf] and Synthetic Ethyl Esters of Plants Oils (Seep Mixture) Drilling Fluids in Deep Water Offshore Environment: Process Variables and Optimization

Recent advances in environmental DNA‐based biodiversity assessment and conservation

Recent advances in environmental DNA‐based biodiversity assessment and conservation

Effect of aerobic water exercise during pregnancy on epidural use and pain: A multi-centre, randomised, controlled trial

ObjectiveThe physical and psychological benefits of exercise during pregnancy are well established. However, the impact of exercise on pain during labour and the use of epidural analgesia has been less explored. The main aim of this study was to analyse the effectiveness and safety of moderate aerobic water exercise by pregnant women on the subsequent use of epidural analgesia during labour, induction of labour, mode of delivery, and pain perception. DesignA multi-centre, parallel, randomised, evaluator blinded, controlled trial in a primary care setting. SettingPrimary care centres in a health district of a tertiary obstetric metropolitan hospital in Mallorca, Spain. ParticipantsPregnant women (14 to 20 weeks’ gestation) who had low risk of complications. MethodsThree hundred and twenty pregnant women were randomly assigned to two groups: women who practiced moderate aquatic aerobic exercise with usual antenatal care, and those who received usual prenatal care alone. The gynaecologist, anaesthesiologist and midwife who assisted the women during labour were blinded to group allocations. Principal outcome: use of epidural analgesia during labour. Other outcomes: use of epidural analgesia before 6 cm cervical dilation, labour pain, type of delivery, time of active labour, episiotomy or perineal tear, and induction of labour. ResultsThe exercise program did not affect the use of epidural analgesia (OR = 0.79, 95% CI = 0.44 to 1.40), vaginal delivery (OR = 1.35, 95% CI = 0.73 to 2.41), or caesarean section (OR = 0.94, 95% CI = 0.47 to 1.89). However, women in the exercise group reported less pain during labour (mean difference: –0.6, 95% CI = –1.11 to –0.09). The two groups (moderate aquatic aerobic exercise versus usual antenatal care) showed no significant differences in maternal or newborn adverse events. ConclusionAquatic aerobic exercise during pregnancy had no effect on the use of epidural analgesia during labour, whereas pain perception was lower after aquatic exercise compared to usual care in pregnancy. The intervention was safe for pregnant women and their newborns.

Effectiveness of Moderate-Intensity Aerobic Water Exercise during Pregnancy on Quality of Life and Postpartum Depression: A Multi-Center, Randomized Controlled Trial.

Background: The global prevalence of postpartum depression is about 20%. This disease has serious consequences for women, their infants, and their families. The aim of this randomized clinical trial was to analyze the effectiveness and safety of a moderate-intensity aerobic water exercise program on postpartum depression, sleep problems, and quality of life in women at one month after delivery. Methods: This was a multi-center, parallel, randomized, evaluator blinded, controlled trial in a primary care setting. Pregnant women (14–20 weeks gestational age) who had low risk of complications and were from five primary care centers in the area covered by the obstetrics unit of Son Llatzer Hospital (Mallorca, Spain) were invited to participate. A total of 320 pregnant women were randomly assigned to two groups, an intervention group (moderate aquatic aerobic exercise) and a control group (usual prenatal care). One month after birth, sleep quality (MOS sleep), quality of life (EQ-5D), and presence of anxiety or depression (EPDS) were recorded. Findings: Women in the intervention group were less likely to report anxiety or depression on the EQ5D (11.5% vs. 22.7%; p < 0.05) and had a lower mean EPDS score (6.1 ± 1.9 vs. 6.8 ± 2.4, p < 0.010). The two groups had no significant differences in other outcomes, maternal adverse events, and indicators of the newborn status. Conclusion: Moderate-intensity aquatic exercise during pregnancy decreased postpartum anxiety and depressive symptoms in mothers and was safe for mothers and their newborns.

A combined management scheme to simultaneously mitigate As and Cd concentrations in rice cultivated in contaminated paddy soil

Paddy soils in southern China are heavily co-polluted by arsenic (As) and cadmium (Cd). The accumulation of these contaminants in rice grains may pose a high health risk. We evaluated the impact of adjusted water management practice (i.e., conventional irrigation and aerobic treatment after heading stage) and the application of two immobilization agents (i.e., CaO and Fe2O3) on the accumulation of As and Cd in rice grains of three rice varieties (i.e., Jinyou-463, Jinyou-268, and Mabayouzhan). The different schemes were tested via conducting a field experiment in paddy soil in Shaoguan, Guangdong Province, China. The results showed that the combined scheme (selecting Jinyou-268, aerobic water management after the heading stage, and 0.09% CaO and 0.5% Fe2O3 amendments) exhibited the best performance in the reduction of As and Cd accumulation in rice grains. This combined scheme decreased the grain As concentration by 26.19% and maintained the Cd at a low level (0.056 mg/kg) as compared to the use of local conventional irrigation patterns. Moreover, health risk assessment demonstrated that by applying the optimal scheme, neither As nor Cd content in rice had carcinogenic risk. However, the grain As remains at a high non-carcinogenic risk. We suggest that future field study design should fully incorporate the uncertainty of the natural environment to make the research conclusions more feasible for popularization and utilization. This study demonstrated an approach of utilizing the synergy effects of various measures for safe rice production in fields subjected to As and Cd contaminations.

Genotypic Differences Among the Rice Genotypes to Arsenic Stress Cultivated Under Two Water Regimes: With an Inference to Human Health

Arsenic (As), a carcinogenic metalloid, is a serious threat to humans due to increased exposure through contaminated water and food. Rice is a staple food and feeds over half of the World's population. Among cereals, rice is more efficient in As uptake and its acquisition into rice grains adversely affect the quality of rice as well as the consumer’s health. The exploitation of genetic variation between rice genotypes for their ability to tolerate water limitations and As accumulation in grains is crucial. The study aimed to investigate the genetic potential of seven rice genotypes for their ability to withstand water limitation (aerobic cultivation) and As toxicity (As-100 µM). The results revealed that under aerobic cultivation system rice genotypes showed less As accumulation in the grains as compared to anaerobic cultivation. Moreover, among all the rice genotypes, less As accumulation in grains was observed in DHAN 140A (2.36 and 3.65 µg g−1) and Shaheen Basmati (2.92 and 3.55 µg g−1), respectively, under aerobic and anaerobic cultivation at high As soil contamination (As-100). Rice genotypes differentially responded against As stress and the cultivation conditions in terms of growth attributes and elemental composition of the plants. Moreover, health risk indices (i.e. ILTCR and HQ) indicate high carcinogenic and non-carcinogenic risks associated with rice consumption grown under high As stress. However, the risks were several folds higher in anaerobically than aerobically cultivated rice genotypes. Among all the genotypes, DHAN 140A indicated less risk, irrespective to the cultivation condition due to decreased As uptake and accumulation of in the grains. The study demonstrated that aerobic water management and selection of genotypes with low As accumulation could be appropriate options to minimize the health risk to human beings.