Evaluation of arsenic effects in Vicia faba by FTIR and FTNIR spectroscopy

Arsenic is an ubiquitous and highly toxic metalloid widely distributed in the environment through
both natural and anthropogenic pathways (Liu et al., 2004) and its presence in food composites is a
matter of concerns to the well being of both humans and animals. In fact, As has been recently
found in drinking water (network and groundwater) in some Italian regions, including Lazio (Central
Italy), at concentration ranging between 25 and 80 μg L-1, higher than the limits set by law (10 μg L-
1) where Arsenic-contaminated groundwaters are often used in agriculture to irrigate crops for food
and animal consumption; this determines that arsenic can enter human food chain. Inorganic or
organic species of the metalloid arsenic occur in the environment. Either inorganic or organic As
occurs in the environment and inorganic forms (iAs) are more toxic than the organic ones (oAs).
Most of the human health effects of arsenic have been established based on epidemiologic studies,
which have shown a significant association between the consumption of arsenic through drinking
water and cancers of the skin, lung, bladder, liver, and kidney, neurologic disease, cardiovascular
disease, as well as other non-malignant diseases. Arsenic is not an essential element for plants and
its over-concentration in soils can generate toxicity phenomena. Its translocation from soil to plant
constitutes one of the main human exposure ways. In this research we evaluated the effects of As
exposure on Vicia faba seedlings by means of infrared (FTIR) and near infrared (FTNIR)
spectroscopy to investigate molecular modifications caused by the interactions of plant with As. Both
techniques showed relevant molecular modifications depending on As exposure. Molecular
modifications evidenced by FTIR spectroscopy were mainly related to modified structures involving
methyl groups of polysaccharides proteins and lipids, resulting better evidenced in meristem root
samples. However, seconds derivative FTIR spectra did not show modification of the secondary
structure of proteins.
The molecular modifications shown by FTNIR spectroscopy were mainly related to the bands of
hydroxyl groups with carboxylic and methyl groups, involving hydrogen bonds between
carbohydrates and nucleic acids and lipids. These molecular and structural modifications are
determined by the direct introduction of As within the plant biomolecules.