A comparative study of the extractability of arsenic species from silverbeet and amaranth vegetables

Abstract

There is still no reliable standard extraction method for the speciation of arsenic (As) in plant tissue, and hence there is great interest in developing one for plants that are used as human food. Speciation and bioavailability are critical for accurate human health risk assessment, as As species vary in both their toxicity and bioavailability. Recent incidences of As poisoning in many countries have led to significant research into the fate and dynamics of As in the soil and water environment, including speciation. Although one of the major pathways of ingestion of As is via food, only limited research has been conducted to assess the nature and proportion of various As species present in food crops. In this study, we compared the efficacy of ammonium dihydrogen phosphate and protein extracting solution for the extractability of As from two different species of spinach (amaranth and silverbeet). We found that a microwave-assisted technique with protein extracting solution was most effective, yielding 76-114% extractability and excellent separation and speciation of all As species present in the spinach matrices. The stability test for extracted As species showed them as stable for 45 days without any significant loss or inter-conversion. Both As III and As V were identified in the shoots of amaranth and silverbeet. However, the percentage of As species varied between amaranth and silverbeet. The silverbeet shoot showed a somewhat higher percentage of As V , while the amaranth showed a higher percentage of As III . The samples contained mostly inorganic As, especially As III ([90%) in the edible part of the vegetables, a form that is more toxic and bioavailable than other organic and methylated species.

Nutritional Components of Amaranth Seeds and Vegetables: A Review on Composition, Properties, and Uses

“…As III and As V were found in the amaranth shoots, the content of As III being higher. Arsenic concentration in spinach of amaranth shoot after acid digestion was 5.6 ± 0.39 μg As/g; inorganic As, especially As III , a more toxic and bioavailable form than organic and methylated species, was prevailing in the edible part (>90%) (Rahman and others ).…”

Arsenic Speciation Analysis by Ion Chromatography - A Critical Review of Principles and Applications

“…A variety of extraction procedure have been developed and optimized for several matrices: terrestrial plants [46][47][48], algae and aquatic plants [49], soils [50][51][52], food [52] and microwave-assisted extraction from soil [53] and vegetables [54,55]. Solvent extraction (SE) are now investigated with a high enrichment factor (115) [56], ultrasound assisted [57,58] and microwave assisted SE [59], solid phase micro-extraction [60][61][62][63][64].…”

The influence of arsenic speciation (AsIII & AsV) and concentration on the growth, uptake and translocation of arsenic in vegetable crops (silverbeet and amaranth): greenhouse study

“…A recent study suggests that As in rice grains is largely present in inorganic forms (Williams et al 2005). Given the significant uptake of As by amaranth and silverbeet and the varying toxicity of different As species, the speciation of As has been investigated in these vegetable crops grown in hydroponic systems (see Rahman et al 2009). …”