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The influx of arsenate, arsenite and dimethyl arsinic acid (DMA) were studied in 7-day-old excised maize roots (Zea mays L.), and then related to arsenate, arsenite and DMA toxicity. Arsenate, arsenite and DMA influx was all found concentration dependent with significant genotypic differences for arsenite and DMA. Arsenate influx in phosphate starved plants best fitted the four-parameter Michaelis-Menten model corresponding to an additive high and low affinity uptake system, while the uptake of phosphate replete plants followed the two parameter model of MichaelisMenten kinetics. Arsenite influx was well described by the two parameter model of 'Michaelis-Menten' kinetics. DMA influx was comprised of linear phase and a hyperbolic phase. DMA influx was much lower than that for arsenite and arsenate. Arsenate and DMA influx decreased when phosphate was given as a pre-treatment as opposed to phosphate starved plants. The +P treatment tended to decrease influx by 50% for arsenate while this figure was 90% for DMA. Arsenite influx increasing slightly at higher arsenite concentrations in P starved plants but at lower arsenite concentrations, there was little or no difference in arsenite uptake. Low toxicity was found for DMA on maize compared with arsenate and arsenite and the relative toxicity of arsenic species was As (V) > As(III) >> DMA.

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Production of biochars from agricultural wastes reduces significantly the volume and weight of the wastes, and hence, it can be considered as a promising means for managing the agricultural wastes. Biochar has received great interest during the last few years, due to its beneficial role to mitigate CO 2 emission through enhancing the long-term carbon sequestration. The effects of biochar on soil properties vary widely, depending on the characteristics of soil and the biochar. Most types of biochars are of alkaline nature and of high C content. Addition of biochar to the soil can improve the cation exchange capacity enrich soil with the nutrients and enhance the microbial growth, and improve some soil physical properties such as water retention and aggregation. For contamination control, biochars have proven to be a suitable tool for controlling the contaminants in the environment. The high surface area, porous structure, alkaline nature, and the presence of functional groups characterized the biochar as alternative option for the remediation of heavy metal contaminated waters and soils. However, there is a lack of knowledge regarding the effects of biochar in the presence of mineral and/or organic fertilizers on the plant growth and nutrient transformation in soils. In addition, biochar is successfully used for treating the acid soils; therefore, future studies are needed to investigate the neutralization of alkaline performance of biochar to be used safely in alkaline soils.

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A UTOMOBILE exhausts are considered the main source of air pollution with heavy metals. Airborne pollutants are precipitated on soils surrounding highways causing serious ecological hazards. The current study aimed at evaluating levels of Pb, Ni, Co and Cd in surface (015-cm) and subsurface (1540-cm) soils nearby Cairo-Alexandria agricultural highway, and their accumulation in plants grown thereon. Seven locations were sampled at interval distances 50 meters on both sides of the highway road near Toukh city (Qualubya Governorate). Cabbage and citrus plants were also sampled and separated into its parts. Results revealed that the investigated soils are contaminated with Pb, Ni and Cd. These contaminants were brought to the subsurface layers of the soil at relatively high concentrations. Total and DTPA-extractable contents of Pb and Ni in the top surface soil decreased with increasing the distance from the high way on both sides of the road. Moreover, concentrations of these metals in the cabbage parts were significantly correlated with their total and DTPA-extractable contents. However, Co and Cd in soils seemed to be not affected by the exhausts of the cars on the highway. Heavy metals decreased in cabbage parts as follows: root > stem > outer leaves > inner leaves > core. Calculated BAF values for Pb, Ni and Co were very low indicating that cabbage might be an excluder for these metals whereas, their transfer from roots to shoots (transfer factor, Ts) were high. Heavy metal concentrations in citrus decreased as leaves > flavedo > albedo > segments. Generally, concentrations of heavy metals in plants particularly Pb exceeded the permissible limits. 19

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