Arsenic-phosphorus interactions in the soil-plant-microbe system: dynamics of uptake, suppression and toxicity to plants

High arsenic (As) concentrations in the soil, water and plant systems can pose a direct health risk to humans and ecosystems. Phosphate (Pi) ions strongly influence As availability in soil, its uptake and toxicity to plants. Better understanding of As(V)-Pi interactions in soils and plants will facilitate a potential remediation strategy for As contaminated soils, reducing As uptake by crop plants and toxicity to human populations via manipulation of soil Pi content. However, the As(V)-Pi interactions in soil-plant systems are complex, leading to contradictory findings among different studies. Therefore, this review investigates the role of soil type, soil properties, minerals, Pi levels in soil and plant, Pi transporters, mycorrhizal association and microbial activities on As-Pi interactions in soils and hydroponics, and uptake by plants, elucidate the key mechanisms, identify key knowledge gaps and recommend new research directions. Although Pi suppresses As uptake by plants in hydroponic systems, in soils it could either increase or decrease As availability and toxicity to plants depending on the soil types, properties and charge characteristics. In soil, As(V) availability is typically increased by the addition of Pi. At the root surface, the Pi transport system has high affinity for Pi over As(V). However, Pi concentration in plant influences the As transport from roots to shoots. Mycorrhizal association may reduce As uptake via a physiological shift to the mycorrhizal uptake pathway, which has a greater affinity for Pi over As(V) than the root epidermal uptake pathway

Speciation of arsenic in tube-well water samples collected from West Bengal, India, by high-performance liquid chromatography-inductively coupled plasma mass spectrometry

The objective of this study was to report on the arsenic species present in tube-well water samples collected from West Bengal, India, especially dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA), whose existence has not been reported in the literature. The water samples were collected from Jalangi Gram Panchayet (Murshidabad district, West Bengal, India). The samples were speciated for arsenic 11 days after collection. The samples were collected in duplicate. One part was acidified with nitric acid (final concentration 0.1%), whereas the other part was left unacidified. A quick and highly sensitive high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICPMS) technique was employed for the separation and detection of the arsenic species. Four arsenic species, namely arsenite [arsenic(III)], DMA, MMA and arsenate [arsenic(V)] were separated and analysed in less than 5 min. Total arsenic concentration was determined by flow injection (FI)-ICPMS. Most of the samples were found to contain low concentrations of DMA and MMA (300 ppb). The existence of DMA and MMA in both acidified and unacidified water samples and in similar concentrations suggests that their presence is natural and not due to acidification. The detection limit of the four arsenic species was 0.06-0.10 ppb. The method was validated by spike recovery and analysis of two water standard reference materials (SRMs). The percentage recoveries of added spikes of all four species were 97-112%. The total arsenic concentration obtained by FI-ICPMS and the sum of the four arsenic species obtained by HPLC-ICPMS for the two water SRMs agreed with the certified values. Moreover, the difference between the total arsenic and the sum of the four arsenic species for most of the water samples was less than 10%. Copyright © 2002 John Wiley & Sons, Ltd