Assessing phytoremediation potentials of selected tropical plants for acrylamide

Abstract

Purpose

Environmentally hazardous and health risk substances in animals and humans in the environment have increased as a result of continuing anthropogenic activities. Examples of these activities are food processing, laboratory, food production, industrial, and other relative activities that use various forms of acrylamide. All acrylamide in the environment are manmade. It is the building block for the polymer, polyacrylamide, which is considered to be a nontoxic additive. However, if the polymerization process is not perfect and complete, the polyacrylamide may still contain acrylamide which is toxic and may pose risks and hazards to the environment. Another form of acrylamide that may pose danger as well in the environment is the acrylamide monomer, which is also a very toxic organic substance that could affect the central nervous system of humans and is likely to be carcinogenic. Phytoremediation could be a tool to somehow absorb this neurotoxic agent and lessen the contamination in the soil. This technology could lessen the soil and water contamination by acrylamide thereby limiting the exposure of animals and humans. This study may also help solve the problem of disposing contaminated acrylamide waste materials. This study was conducted to achieve the following objectives: (1) to evaluate phytoremediation potentials of some selected tropical plants in acrylamide-contaminated soil, (2) to compare the performance of tropical plants in absorbing acrylamide through accumulation in their roots and shoots, and (3) to determine the outcome of acrylamide in the soil after treatment using the test plants with phytoremediation potentials.

Materials and methods

Soil was collected from 40 sampling points (2,000 g of soil per sampling points) in a half-hectare rice field in the Philippine Rice Research Institute, Central Experiment Station, Science City of Muñoz, Nueva Ecija, Philippines. This study used Mustard (Brassica juncea L.), petchay (Brassica chinensis L.), vetiver grass (Vetiveria zizanioides L.), hog weeds (Portulaca oleracea L.), snake plant (Sanseviera trifasciata Prain), and common sword fern (Nephrolepsis cordifolia L.). These plants were selected to determine their capability of removing acrylamide residues from soil with unstable polyacrylamide gel. Analysis of acrylamide concentrations in soil and plant parts were done using a gas chromatograph equipped with flame ionization detector at the Training, Research and Development, Adamson University, Manila. This study was laid out using the completely randomized design with three replications. Data were analyzed with a one-way ANOVA using PROC GLM. Duncan’s multiple range test (p ≤ 0.05) was followed for the mean treatment separation and comparison.

Results and discussion

Among the plants tested, the highest concentration of acrylamide was absorbed by the whole plant of mustard (6,512.8 mg kg⁻¹) compared with pechay (3,482.7 mg kg^–1), fern (2,015.4 mg kg^–1), hogweeds (1,805.3 mg kg^–1), vetiver grass (1,385.4 mg kg^–1), and snake plants (887.5 mg kg^–1). Results of the study regarding the acrylamide absorption of the whole plants of mustard and pechay conformed to previous findings of other studies. Two members of the Brassica family, B. juncea L. (mustard) and B. chinensis L. (pechay) were found to be effective in removing wide ranges of contaminants. Likewise, mustard obtained the highest acrylamide concentrations (mg kg^–1) in the roots (2,372.9) and shoots (4,081.1) among the six test plants. Earlier studies showed the capability of mustard in absorbing metals. Mustard plant is known to remove large quantities of chromium, lead, copper, and nickel in soil and ethidium bromide in soil. This could be attributed to its well-developed root system. Plants with active growth of roots in soils bring more contact with the fresh areas of the soil and ions, thus, creating more likelihood of further absorption and uptake. Moreover, mustard, pechay, and fern plants had 60% survival rate while hogweeds had 80% survival rate. Snake plant and vetiver grass had 100% survival rate. All the test plants planted in soil without acrylamide had survival rate of 100%. The 100% survival rate of vetiver grass and snake plant was due to the tolerance of these plants to acrylamide. Among the six test plants, vetiver grass and snake plant had the greatest uptake of acrylamide from the soil (30.6 kg ha^–1) and (29.4 kg ha^–1), respectively. These plants exhibited great number and longer roots which are characteristics of excellent phytoremediator plants. Thus, vetiver grass can absorb more acrylamide due to its root’s growth characteristics. These findings could be attributed to the extraordinary features of vetiver grass such as its massive and deep root system and heavy biomass including its high tolerance to extreme soil conditions like heavy metal toxicities and high metal concentration.

Conclusions

Results of our study proved that all the test plants are potential phytoremediators of acrylamide. However, mustard and pechay were the most effective as they absorbed the highest acrylamide concentrations in their roots, shoots, and the whole plants. On the other hand, vetiver grass and snake plant had the highest uptake of acrylamide even though these plants did not absorb the highest acrylamide concentration. Therefore, these two plants can be considered as the best phytoremediator of acrylamide because they are perennial plants with heavier biomass with long, dense and extended root system. As such, these plants are capable of absorbing acrylamide in the soil for a long period of time. As preventive measures and for application purposes, vetiver grass and snake plants could be planted along and around the wastewater treatment ponds of laboratories using polyacrylamide gel. These plants can prevent further migration of pollutants to the environment aside from making the ponds more resistant to soil erosion. Further studies are suggested to evaluate acrylamide contaminations from laboratory washing, primary treatment pond, and seepage ponds that have earth dikes. Vetiver grass and snake plants are recommended for further phytoremediation studies for longer period of time to test the reduction of acrylamide in soil. Moreover, the outcome of acrylamide accumulation in the plants is also recommended for further study in conjunction with labeled-carbon tracer to determine its effects on the plants.