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Arsenic (As) contamination is a widespread problem. Continued and concerted effort in exploring sustainable remediation strategies is required, with in-situ immobilization emerging as a promising option. This work valorized a waste by-product from olive milling into functional hydrochar. The hydrochar was then transformed into iron oxide encapsulated carbon with three different iron loading rates (10%, 25%, and 50% w/w of iron chloride hexahydrate added to the olive mill waste feedstock). Both the hydrochar and the three iron oxide encapsulated carbon materials were then tested, in a pot trial using a 3% w/w application rate, as a means to immobilize As in a mining contaminated soil (2580±110 mg/kg As). After a 45-day incubation period, the effect of adding the amendments on arsenic mobility and bioaccessibility compared to an untreated control was measured using a sequential extraction procedure (SEP) and in vitro bioaccessibility (IVBA), respectively. All four treatments resulted in a decrease in mobility and in vitro bioaccessibility as compared with the control. Specifically, As in the mobile phases was up to 35% less than the in control, while bioaccesibility was 21.8% in the control and ranged from 17.5 to 12.3% in the treatments. The efficiency of amendments to immobilize As increased with the iron content of the developed materials. This work positions hydrochars and iron oxide encapsulated carbon materials produced from olive mill waste as promising options to immobilise As in-situ. This article is protected by copyright. All rights reserved.

In recent times, there has been increased focus on a holistic approach to soil remediation with consideration of social, economic and environmental factors. Consequently, there is a demand from practitioners and regulators alike for suitable ways to measure ancillary outcomes, for example, effects on soil quality. Here we show that biochar, when applied to land to remediate lead (Pb)-contaminated soils, can lead to environmental improvements not realized by adding mined or manufactured phosphates. Here, we study a Pb-contaminated soil amended with two phosphate fertilizers (slow- and fast-release) and with biochars produced from poultry litter and from biosolids at three temperatures (300 &deg, C, 400 &deg, C and 500 &deg, C). The results show that, unlike the fast-release P fertilizer, biochars did not result in an increase in the amount of leachable P that could be released into the environment. Biochars prepared at 500 &deg, C presented a higher value of the integrative geometric mean of soil enzyme activity, compared to the P fertilizers. Overall, our research shows that biochars, particularly those prepared at the higher temperature tested, are a suitable alternative to P fertilizers as an integrative remediation strategy in Pb-contaminated soils, enabling soil biological restoration.

Urban soils in many communities in the United States and internationally have been contaminated by lead (Pb) from past use of lead additives in gasoline, deterioration of exterior paint, emissions from Pb smelters and battery recycling and other industries. Exposure to Pb in soil and related dust is widespread in many inner city areas. Up to 20–40% of urban children in some neighborhoods have blood lead levels (BLLs) equal to or above 5 μg per decilitre, the reference level of health concern by the U.S. Centers for Disease Control. Given the widespread nature of Pb contamination in urban soils it has proven a challenge to reduce exposure. In order to prevent this exposure, an evidence-based approach is required to isolate or remediate the soils and prevent children and adult's ongoing exposure. To date, the majority of community soil Pb remediation efforts have been focused in mining towns or in discrete neighborhoods where Pb smelters have impacted communities. These efforts have usually entailed very expensive dig and dump soil Pb remediation techniques, funded by the point source polluters. Remediating widespread non-point source urban soil contamination using this approach is neither economical nor feasible from a practical standpoint. Despite the need to remediate/isolate urban soils in inner city areas, no deliberate, large scale, cost effective Pb remediation schemes have been implemented to isolate inner city soils impacted from sources other than mines and smelters. However, a city-wide natural experiment of flooding in New Orleans by Hurricane Katrina demonstrated that declines in soil Pb resulted in major BLL reductions. Also a growing body of literature of smaller scale pilot studies and programs does exist regarding low cost efforts to isolate Pb contaminated urban soils. This paper reviews the literature regarding the effectiveness of soil Pb remediation for reducing Pb exposure and BLL in children, and suggests best practices for addressing the epidemics of low-level Pb poisoning occurring in many inner city areas.

A phytoextraction experiment with five Cd hyperaccumulators (Amaranthus hypochondriacus, Celosia argentea, Solanum nigrum, Phytolacca acinosa and Sedum plumbizincicola) was conducted in two soils with different soil pH (5.93 and 7.43, respectively). Most accumulator plants grew better in the acidic soil, with 19.59–39.63% higher biomass than in the alkaline soil, except for S. plumbizincicola. The potential for a metal-contaminated soil to be cleaned up using phytoremediation is determined by the metal uptake capacity of hyperaccumulator, soil properties, and mutual fitness of plant-soil relationships. In the acidic soil, C. argentea and A. hypochondriacus extracted the highest amount of Cd (1.03 mg pot−1 and 0.92 mg pot−1, respectively). In the alkaline soil, S. plumbizincicola performed best, mainly as a result of high Cd accumulation in plant tissue (541.36 mg kg−1). Most plants achieved leaf Cd bioconcentration factor (BCF) of >10 in the acidic soil, compared to

Transformation of soil Pb to pyromorphites and phosphates has the potential to be an effective strategy to immobilize this contaminant in situ. Soil treatment using monocalcium phosphate, a commercial fertilizer (NTS Soft Rock) and biochars prepared from poultry litter and from biosolids at three different temperatures (300, 400, and 500°C) and two doses (1 and 3%) were evaluated. Lead bioaccesibility, mobility, and solid speciation were measured. Leachable Pb (determined with the toxicity characterized leaching procedure) was not significantly ( > 0.05) changed after biochar addition, but a significant decrease in bioaccesible Pb was found for several treatments ( < 0.05). This was particularly notable for treatments receiving biosolids prepared at 400 and at 500°C or monocalcium phosphate at the 3% dose. The decrease in bioaccesible Pb concentration in the biochar treatments was similar to traditional phosphate amendments. Our research found transformation of Pb species to the more stable pyromorphite and Pb-phosphate to be partially responsible for the observed changes, although other mechanisms, including pH changes, might also play an important role. Overall, pyrolysis was an effective method to upgrade waste streams and facilitate Pb immobilization, although key pyrolysis parameters need to be selected carefully.