Effect of mineral-based amendments on rice (Oryza sativa L.) growth and cadmium content in plant and Polluted soil

Agricultural soils can be contaminated by industrial activities such as mining and smelting. Contamination with cadmium (Cd) can significantly exceed average background values, which can lead to uptake by rice plant and even harm to humans through food chain. In Hunan province, southern China, rice (Oryza sativa L.) is the main cereal, and human exposure to metallic contaminants through rice pathway is of particular interest. Shortage of land for rice growing means that contaminated agricultural soil is still cultivated for rice in Hunan. In the present work, a field experiment was undertaken to remediate Cd-contaminated paddy soil with three mineral amendments, namely sepiolite, bone char, and a silicon-based product (normally used as fertilizer). Average Cd concentration in the paddy soil was 2.85 mg/kg, significantly exceeding Chinese soil quality standards of China. Cd content was 0.59 mg/kg in sepiolite, 0.28 mg/kg in bone char, and 0.44 mg/kg in silicon fertilizer, respectively. Distribution fractions of Cd in soil followed the order of exchangeable (FI) > organic matter-bound (FIII) > residual (FIV) > oxide-bound (FII) without treatment, while exchangeable (FI) > residual (FIV) > organic matter-bound (FIII) > oxide-bound (FII) after treatment. With addition of three amendments, soil pH values and rice growth such as plant height and ripening rate increased. Concentrations of Cd in the rice plant (straw, husk, and unpolished rice) decreased after treatment. However, among three amendments, only the bone char addition reduced Cd accumulation in the rice plant below the Chinese standard value (0.2 mg/kg) and in the husk to below the Chinese feed hygiene standard for food (0.5 mg/kg)

Mitigating heavy metal accumulation into rice (Oryza sativa L.) using biochar amendment — a field experiment in Hunan, China

A field experimentwas conducted to investigate the effect of bean stalk (BBC) and rice straw (RBC) biochars on the bioavailability of metal(loid)s in soil and their accumulation into rice plants. Phytoavailability of Cd was most dramatically influenced by biochars addition. Both biochars significantly decreased Cd concentrations in iron plaque (35–81 %), roots (30–75 %), shoots (43–79 %) and rice grain (26–71 %). Following biochars addition, Zinc concentrations in roots and shoots decreased by 25.0–44.1 and 19.9–44.2 %, respectively, although no significant decreases were observed in iron plaque and rice grain. Only RBC significantly reduced Pb concentrations in iron plaque (65.0 %) and roots (40.7 %). However, neither biochar significantly changed Pb concentrations in rice shoots and grain. Arsenic phytoavailability was not significantly altered by iochars addition. Calculation of hazard quotients (HQ) associated with rice consumption revealed RBC to represent a promising candidate to mitigate hazards associated with metal(loid) bioaccumulation. RBC reduced Cd HQ from a 5.5 to 1.6. A dynamic factor’s way was also used to evaluate the changes in metal(loid) plant uptake process after the soil amendment with two types of biochar. In conclusion, these results highlight the potential for biochar to mitigate the phytoaccumulation of metal(loid)s and to thereby reduce metal(loid) exposure associated with rice consumption

Black carbon (BC) in a northern Tibetan mountain: effect of Kuwait fires on glaciers

The black carbon (BC) deposition on the ice core at Muztagh Ata Mountain, northern Tibetan Plateau, was analyzed. Two sets of measurements were used in this study, which included the air samplings of BC particles during 2004-2006 and the ice core drillings of BC deposition during 1986-1994. Two numerical models were used to analyze the measured data. A global chemical transportation model (MOZART-4) was used to analyze the BC transport from the source regions, and a radiative transfer model (SNICAR) was used to study the effect of BC on snow albedo. The results show that during 1991-1992, there was a strong spike in the BC deposition at Muztagh Ata, suggesting that there was an unusual emission in the upward region during this period. This high peak of BC deposition was investigated by using the global chemical transportation model (MOZART-4). The analysis indicated that the emissions from large Kuwait fires at the end of the first Gulf War in 1991 caused this high peak of the BC concentrations and deposition (about 3-4 times higher than other years) at Muztagh Ata Mountain, suggesting that the upward BC emissions had important impacts on this remote site located on the northern Tibetan Plateau. Thus, there is a need to quantitatively estimate the effect of surrounding emissions on the BC concentrations on the northern Tibetan Plateau. In this study, a sensitivity study with four individual BC emission regions (Central Asia, Europe, the Persian Gulf, and South Asia) was conducted by using the MOZART-4 model. The result suggests that during the "normal period" (non-Kuwait fires), the largest effect was due to the Central Asia source (44 %) during the Indian monsoon period, while during the non-monsoon period, the largest effect was due to the South Asia source (34 %). The increase in radiative forcing increase (RFI) due to the deposition of BC on snow was estimated by using the radiative transfer model (SNICAR). The results show that under the fresh snow assumption, the estimated increase in RFI ranged from 0.2 to 2.5 W m(-2), while under the aged snow assumption, the estimated increase in RFI ranged from 0.9 to 5.7 W m(-2). During the Kuwait fires period, the RFI values increased about 2-5 times higher than in the "normal period", suggesting a significant increase for the snow melting on the northern Tibetan Plateau due to this fire event. This result suggests that the variability of BC deposition at Muztagh Ata Mountain provides useful information to study the effect of the upward BC emissions on environmental and climate issues in the northern Tibetan Plateau. The radiative effect of BC deposition on the snow melting provides important information regarding the water resources in the region

Measuring and Modeling Black Carbon (BC) Contamination in the SE Tibetan Plateau,

Black carbon (BC) concentrations were measured in the southeast (SE) Tibetan Plateau along the valley of the Yarlung Tsangpo River during winter (between November, 2008 and January, 2009). The measured mean concentration (0.75 &mu;g m&minus;3) is significantly higher than the concentrations (0.004&ndash;0.34 &mu;g m&minus;3) measured in background and remote regions of the globe, indicating that Tibetan glaciers are contaminated by BC particles in the Plateau. Because BC particles play important roles for the climate in the Tibetan Plateau, the sources and causes of the BC contamination need to be understood and investigated. In this study, a mesocale dynamical model (WRF) with BC particle modules is applied for analyzing the measurement. The analysis suggests that the major sources for the contamination in the SE Plateau were mainly from the BC emissions in eastern Indian and Bangladesh. Because of the west prevailing winds, the heavy emissions in China had no significant effects on the SE Plateau in winter. Usually, the high altitude of the Himalayas acts a physical wall, inhibiting the transport of BC particles across the mountains to the plateau. This study, however, finds that the Yarlung Tsangpo River valley causes a &#39;leaking wall&#39;, whereby under certain meteorological conditions, BC particles are being transported up onto the glacier. This too causes variability of BC concentrations (ranging from 0.3 to 1.5 &mu;g m&minus;3) in a time scale of a few days. The analysis of the variability suggests that the &ldquo;leaking wall&rdquo; effect cannot occur when the prevailing winds were northwest winds, during which the BC transport along the valley of the Yarlung Tsangpo River was obstructed. As a result, large variability of BC concentration was observed due to the change of prevailing wind directions.</p

Two distinct patterns of seasonal variation of airborne black carbon overTibetan Plateau

Airborne black carbon (BC) mass concentrations were measured from November 2012 to June 2013 at Ranwu and Beiluhe, located in the southeastern and central Tibetan Plateau, respectively. Monthly mean BC concentrations show a winter (November&ndash;February) high (413.2 ng m&minus;3) and spring (March&ndash;June) low (139.1 ng m&minus;3) at Ranwu, but in contrast a winter low and spring high at Beiluhe (204.8 and 621.6 ng m&minus;3, respectively). By examining the meteorological conditions at various scales, we found that the monthly variation of airborne BC over the southeastern Tibetan Plateau (TP) was highly influenced by regional precipitation and over the hinterland by winds. Local precipitation at both sites showed little impact on the seasonal variation of airborne BC concentrations. Potential BC source regions are identified using air mass backward trajectory analysis. At Ranwu, BC was dominated by the air masses from the northeastern India and Bangladesh in both winter and spring, whereas at Beiluhe it was largely contributed by air masses from the south slope of Himalayas in winter, and from the arid region in the north of the TP in spring. The winter and spring seasonal peak of BC in the southern TP is largely contributed by emissions from South Asia, and this seasonal variation is heavily influenced by the regional monsoon. In the northern TP, BC had high concentrations during spring and summer seasons, which is very likely associated with more efficient transport of BC over the arid regions on the north of Tibetan Plateau and in Central Asia. Airborne BC concentrations at the Ranwu sampling site showed a significant diurnal cycle with a peak shortly after sunrise followed by a decrease before noon in both winter and spring, likely shaped by local human activities and the diurnal variation of wind speed. At the Beiluhe sampling site, the diurnal variation of BC is different and less distinct.</p

Black carbon (BC) in a northern Tibetan mountain: effect of Kuwait fires on glaciers

The black carbon (BC) deposition on the ice core at Muztagh Ata Mountain, northern Tibetan Plateau, was analyzed. Two sets of measurements were used in this study, which included the air samplings of BC particles during 2004&ndash;2006 and the ice core drillings of BC deposition during 1986&ndash;1994. Two numerical models were used to analyze the measured data. A global chemical transportation model (MOZART-4) was used to analyze the BC transport from the source regions, and a radiative transfer model (SNICAR) was used to study the effect of BC on snow albedo. The results show that during 1991&ndash;1992, there was a strong spike in the BC deposition at Muztagh Ata, suggesting that there was an unusual emission in the upward region during this period. This high peak of BC deposition was investigated by using the global chemical transportation model (MOZART-4). The analysis indicated that the emissions from large Kuwait fires at the end of the first Gulf War in 1991 caused this high peak of the BC concentrations and deposition (about 3&ndash;4 times higher than other years) at Muztagh Ata Mountain, suggesting that the upward BC emissions had important impacts on this remote site located on the northern Tibetan Plateau. Thus, there is a need to quantitatively estimate the effect of surrounding emissions on the BC concentrations on the northern Tibetan Plateau. In this study, a sensitivity study with four individual BC emission regions (Central Asia, Europe, the Persian Gulf, and South Asia) was conducted by using the MOZART-4 model. The result suggests that during the &ldquo;normal period&rdquo; (non-Kuwait fires), the largest effect was due to the Central Asia source (44 %) during the Indian monsoon period, while during the non-monsoon period, the largest effect was due to the South Asia source (34 %). The increase in radiative forcing increase (RFI) due to the deposition of BC on snow was estimated by using the radiative transfer model (SNICAR). The results show that under the fresh snow assumption, the estimated increase in RFI ranged from 0.2 to 2.5 W m&minus;2, while under the aged snow assumption, the estimated increase in RFI ranged from 0.9 to 5.7 W m&minus;2. During the Kuwait fires period, the RFI values increased about 2&ndash;5 times higher than in the &ldquo;normal period&rdquo;, suggesting a significant increase for the snow melting on the northern Tibetan Plateau due to this fire event. This result suggests that the variability of BC deposition at Muztagh Ata Mountain provides useful information to study the effect of the upward BC emissions on environmental and climate issues in the northern Tibetan Plateau. The radiative effect of BC deposition on the snow melting provides important information regarding the water resources in the region.</p