Metal Accumulation In Crops Research Articles

Bacterial community shaped by heavy metals and contributing to health risks in cornfields

Scientists are increasingly aware that heavy metal contamination in soils, especially in farmland ecosystems, can negatively affect human health and alter the bacterial community that plays a critical role in plant growth and heavy metal accumulation. The goal of the present paper was to uncover how various heavy metals and non-metallic elements affect human health and bacterial diversity in cornfields and to explore the contribution of soil bacteria to heavy metal accumulation in crops. Soil samples were collected from five counties in Shandong Province, China, where abnormally high levels of heavy metals and metalloids were caused by mining and heavy industry. We calculated a hazard quotient (HQ) to evaluate the health risk these heavy metals cause and analyzed the soil bacterial community using 16S rRNA gene sequencing. The HQ results showed that As posed the greatest threat to human health followed by Pb although concentrations of all metals did not reach the health risk threshold. Meanwhile, principal component analysis (PCA) and redundancy analysis (RDA) revealed soil bacterial richness was significantly influenced by As, Ni, and Cr as well as pH and phosphorus, but not by the species diversity of aboveground weeds. The most abundant bacteria in our study region were heavy metal tolerant groups, specifically Actinobacteria and Proteobacteria. Moreover, correlation analysis suggested that Actinobacteria might reduce the phytoaccumulation of Cr, Cu, Zn, and Hg in corn, while Proteobacteria might weaken phytoaccumulation of Pb, Ni, As, and Cd. Our results verified that heavy metals play an important role in shaping the soil bacterial community. Using native bacteria in farmland provides a potential biological strategy for reducing the health risk posed by heavy metals related to food consumption.

Atmospheric heavy metal deposition in agro-ecosystems in China

Atmospheric deposition has become one of the main sources of heavy metals in crops in developed and industrial zones in China for the past several years. However, lack of data of the agro-ecosystems on the vast areas of China makes it difficult to assess the impacts of air pollution on the heavy metal accumulation in crops. In this study, with deposit samples from 67 sites located at different agro-ecosystems (typical, factory nearby, town nearby, roadside, and remote) of four natural regions [Huanghuai (HH), Southeast (SE), Southwest (SW) and upper-mid Yangzi River (Up-mid YR)], atmospheric heavy metal deposition in agro-ecosystems on a large scale in China was studied. The results showed that during the growing season, the deposition fluxes of Cr, Ni, As, Cd, and Pb in typical agro-ecosystems were 0.60-36.86, 0.65-25.37, 0.05-8.88, 0.12-5.81, and 0.43-35.63μgm-2day-1, respectively, which varied greatly between the four different regions. The average deposition fluxes of Cr, Ni, Cd, and Pb in the HH region, as well as the fluxes of As in the SW region, were significantly higher than those in the SE region. Heavy metal deposition rates among agro-ecosystems were very similar, except for the sites around cement factory in flat HH region. In mountainous SW region, however, deposition rates varied widely with sites nearby towns relatively higher and remote regions much lower. Higher correlation coefficients were observed between Cr, As, Pb, and Ni deposition rates, suggesting that they had similar sources. Samples from the SW and SE regions exhibited higher 207Pb/206Pb and 208Pb/206Pb ratios than those from the HH and Up-mid YR regions. Airborne Pb in SW agro-ecosystems were mainly derived from vehicle exhaust and local smelting, whereas that in the HH region from burning of northern Chinese coal.

Challenges in assessing the health risks of consuming vegetables in metal-contaminated environments

A great deal of research has been devoted to the characterization of metal exposure due to the consumption of vegetables from urban or industrialized areas. It may seem comforting that concentrations in crops, as well as estimated exposure levels, are often found to be below permissible limits. However, we show that even a moderate increase in metal accumulation in crops may result in a significant increase in exposure. We also highlight the importance of assessing exposure levels in relation to a regional baseline. We have analyzed metal (Pb, Cd, As) concentrations in nearly 700 samples from 23 different vegetables, fruits, berries and mushrooms, collected near 21 highly contaminated industrial sites and from reference sites. Metal concentrations generally complied with permissible levels in commercial food and only Pb showed overall higher concentrations around the contaminated sites. Nevertheless, probabilistic exposure assessments revealed that the exposure to all three metals was significantly higher in the population residing around the contaminated sites, for both low-, median- and high consumers. The exposure was about twice as high for Pb and Cd, and four to six times as high for As. Since vegetable consumption alone did not result in exposure above tolerable intakes, it would have been easy to conclude that there is no risk associated with consuming vegetables grown near the contaminated sites. However, when the increase in exposure is quantified, its potential significance is harder to dismiss – especially when considering that exposure via other routes may be elevated in a similar way.

Impact of Heavy Metal Containing Wastewater on Agricultural Soil and Produce: Relevance of Biological Treatment

Increasing discharge of heavy metals in water and soil from different sources is a matter of concern for the environment and health safety. Irrigation with heavy metal contaminated water can deteriorate the quality of soil as well as the agricultural produce. In the present study, the scenario of heavy metal contamination in water bodies has been reviewed and the impact of heavy metals on various soil properties such as carbon mineralization, microbial biomass, enzymes activities, nitrogen fixation, pH and cation exchange capacity (CEC) has been analysed. Subsequently, metal accumulation in crops has been surveyed and in some cases concentrations of these heavy metals in edible part of crops were found higher than the prescribed guidelines by various government agencies. Recently, developed biological methods at lab and pilot level for remediation of heavy metals, and the challenges for implementation of these technologies, have also been discussed in this mini-review.

Characteristics of heavy metal transfer and their influencing factors in different soil–crop systems of the industrialization region, China

Soil heavy metals and their bioaccumulation in agricultural products have attracted widespread concerns, yet the transfer and accumulation characteristics of heavy metals in different soil–crop systems was rarely investigated. Soil and crop samples were collected from the typical agricultural areas in the Yangtze River Delta region, China. The concentrations of Cu, Pb, Zn, Cd and Hg in the soils, roots and grains of rice (Oryza Sativa L.), wheat (Triticum L.) and canola (Brassica napus L.) were determined in this study. Transfer ability of heavy metals in soil-rice system was stronger than those in soil-wheat and soil-canola systems. The wheat showed a strong capacity to transfer Zn, Cu and Cd from root to the grain while canola presented a restricting effect to the intake of Cu and Cd. Soil pH and total organic matter were major factors influencing metal transfer from soil to rice, whereas soil Al2O3 contents presented a negative effect on heavy metal mobility in wheat and canola cultivation systems. The concentration of Zn and Cd in crop grains could well predicted according to the stepwise multiple linear regression models, which could help to quantitatively evaluate the ecologic risk of heavy metal accumulation in crops in the study area.

Phytoaccumulation of Heavy Metals in Natural Vegetation at the Municipal Wastewater Site in Abbottabad, Pakistan

Heavy metal accumulation in crops and soils from wastewater irrigation poses a significant threat to the human health. A study was carried out to investigate the removal potential of heavy metals (HM) by native plant species, namely Cannabis sativa L., Chenopodium album L., Datura stramonium L., Sonchus asper L., Amaranthus viridus L., Oenothera rosea (LHer), Xanthium stramonium L., Polygonum macalosa L., Nasturtium officinale L. and Conyza canadensis L. growing at the municipal wastewater site in Abbottabad city, Pakistan. The HM concentrations varied among plants depending on the species. Metal concentrations across species varied in the order iron (Fe) > zinc (Zn) > chromium (Cr) > nickel (Ni) > cadmium (Cd). Majority of the species accumulated more HM in roots than shoots. Among species, the concentrations (both in roots and shoots) were in the order C. sativa > C. album > X. stramonium > C. canadensis > A. viridus > N. officinale > P. macalosa > D. stramonium > S. asper > O. rosea. No species was identified as a hyperaccumulator. All species exhibited a translocation factor (TF) less than 1. Species like C. sativa, C. album and X. stramonium gave higher (> 1) biological concentration factor (BCF) and biological accumulation coefficient (BAC) especially for Fe, Cr and Cd than other species. Higher accumulation of heavy metals in these plant species signifies the general application of these species for phytostabilization and phytoextraction of HM from polluted soils.

Adaptation Strategies of Plants against Heavy Metal Toxicity: A Short Review

Significant amounts of heavy metals have been added to the soils globally due to the natural as well as anthropogenic activities. The heavy metal accumulation in crops may cause serious disorders in plants as well as in human beings. Therefore, investigation on heavy metals toxicity is remaining an area of scientific interest. In order to increase crop productivity and minimizing health hazards of heavy metals toxicities it is necessary to understand their mechanisms of toxicity. In this way, osmolytes such as proline is endogenous organic substance which regulates normal growth and development of plants, grown under metal contaminated urban and peri-urban areas. Therefore, application of proline and/or manipulation of gene(s) enhance the activity of enzyme(s) and their biosynthetic pathways have also been found to be much effective in mitigating heavy metal toxicity. In this review, impact of heavy metal toxicity on plants and adaptation strategies of plants with special role of proline have briefly been discussed.

RNA Interference‐mediated Silencing of Phytochelatin Synthase Gene Reduce Cadmium Accumulation in Rice Seeds

Abstract Phytochelatins (PCs) play an important role in heavy metal resistance and accumulation. To reduce the accumulation of cadmium (Cd) in rice seeds, the expression of phytochelatin synthase (PCS) gene OsPCS1 was suppressed by RNA interference (RNAi). A hairpin construct of a PCS fragment was designed in the pRNAi‐OsPCS1 under the control of ZMM1, a seed‐specific promoter from maize. The construct was introduced into rice (japonica) through Agrobacterium tumefaciens. The RNAi rice plantlets were selected and cultivated in pots exposured to 10 mg/kg Cd. The transcriptional level of OsPCS1 declined in seeds of some RNAi rice compared to the wild type. As a result Cd accumulation was reduced by about half in the seeds of RNAi rice. As expected, no apparent difference of growth appeared between RNAi and wild‐type plants. The results suggest that this new approach can be used to control heavy metal accumulation in crops.

Influence of Soil Amendments on Heavy Metal Accumulation in Crops on Polluted Soils of Bangladesh

Pot experiments with soils from three contaminated sites and an additional field experiment were conducted. The aim of the experiments was to test different organic and inorganic soil amendments to heavy metal uptake and to alleviate toxicity in different agricultural crops. Elements in the extracts were measured by plasma emission spectroscopy (ICP‐AES). Cadmium in the extracts was measured by atomic absorption spectroscopy (AAS), with a heated graphite‐tube system (HGA). The results of the experiment were statistically evaluated by the LSD test. Almost all treatments had positive effects on crop productivity or reduced heavy metal uptake. Organic manures especially reduced manganese (Mn), chromium (Cr), and nickel (Ni) uptake. Iron (Fe) oxides contained in red mud, a by-product of the aluminum industry, reduced soil to plant transfer of zinc (Zn), Ni, cadmium (Cd), and Cr. The results from these experiments show that it is necessary to select and combine amendments taking into account both site and crop characteristics.

Potential benefits and inherent dangers in cropping municipal waste dump sites – case studies in the City of Ibadan, Nigeria

The benefits derivable to crops from the high fertility status of municipal wastes dump sites and the dangers of heavy metal accumulation in crops planted therein were examined in three municipal refuse dumpsites namely, [Eleiyele (Site 1), Ring Road, (Site 2) and Bere (Site 3)] in Ibadan, Nigeria. The response of maize (Zea mays) to the soil nutrients and heavy metals were examined in the greenhouse and in the field. The plant nutrients in the three dump sites were quite adequate for maize growth and development but no germination of the test crop was observed in Site 3. Water (absorbed) and potassium nitrate (KNO3) (exchangeable) fractions of the heavy metals in the soils of the three sites were lower than the critical levels considered to be phytotoxic. However, the total extractable copper (Cu) (20.42mgkg-1) and zinc (Zn) (39.44mgkg-1) in the soils were higher in Site 3 than in the other dump sites. Site 3 soil also contained the highest population of cellulose degrading microorganisms. The concentrations of the heavy metals in plant tissue planted in the greenhouse experiment were low but high in plant tissue harvested in the field. Refuse dump site soils are important in Ibadan agricultural production but it is necessary that cropping is preceeded by soil test to determine nutrient and heavy metal concentrations. Keywords:Soil nutrients; Fertility status; Heavy metals; Municipal wastes [Global Jnl Environ Sci Vol.2(2) 2003: 102-105]