Document Type : Research Paper

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Accumulation and distribution of heavy metals in coriander plant (Coriandrum sativum L.) under the influence of irrigation with treated municipal wastewater

EXTENDED ABSTRACT

Introduction

Iran, as one of the arid and semi-arid regions of the world, is facing a drastic decrease in renewable water resources, and the demand for high-quality water in this country is expected to increase. This has forced the decision makers to preserve better quality water resources for urban and drinking purposes and less quality water resources (such as reclaimed wastewater) to be allocated for purposes such as irrigation of crops, vegetables and green spaces. In the meantime, the accumulation of heavy metals within different tissues of the crops and vegetables (especially leafy ones) irrigated with reclaimed wastewater, is still unclear. Therefore, the concentration of these metals in the plants should be measured and monitored, regularly due to their risk of entering the human food cycle and bringing about diseases. Hence, in this study, the effects of irrigation with treated municipal wastewater on the accumulation of heavy metals in the roots and aerial parts of the coriander plant (Coriandrum sativum L.) were investigated and compared with that in coriander irrigated with well water (control treatment).

Materials and Methods

This research was conducted in Kermanshah city with a semi-arid-cold climate. Kermanshah municipal wastewater treatment plant is located in the southwest of the city with an area of 78 hectares. This treatment plant collects wastewater from a population of 400,000 people, so its daily discharge capacity is 60,000 cubic meters. The treatment process in this wastewater treatment plant is a conventional activated sludge method. In this research, the fields under coriander cultivation were located at the downstream of the treatment plant, each with an area of nearly 5 hectares. The lands under irrigation with treated wastewater were always irrigated with the effluents of the treatment for nearly 20 years, and the control treatments, were also irrigated with well water for many years. At the time of harvesting, a number of whole coriander plants (roots and aerial parts) from different parts of each treatment were randomly harvested in three replicates. The different parts of each plant were washed to eliminate possible pollutants. Then, the drying process of the plant samples was carried out. Finally, different parts of each plant, including aerial parts and roots were crushed and ground. Plant samples were digested using the method described by Batarse et al. (2011). An atomic absorption device (Spectra AA 220 model) was used to measure the concentration of heavy metals in samples. The experimental design was carried out in three replications in a completely randomized design (CRD) arrangement with two irrigation treatments including irrigation with reclaimed wastewater and irrigation with well water. Data were analyzed using Minitab 16.2.4. The mean comparison test was performed at 1 and 5% of probability levels using Tukey's method.

Results and discussion

The results showed that the concentration of all investigated heavy metals in different parts (roots and aerial parts) of coriander plant irrigated with reclaimed wastewater was significantly higher than that of the control treatment (irrigated with well water). However, fortunately, the concentration of all these metals within all the plant parts of the coriander plant was evaluated to be lower than the permissible levels for heavy metals in vegetables. Therefore, in the current situation of the shortage of water resources in Kermanshah province, reclaimed wastewater provides a unique and viable supply of water for the irrigation of vast areas of coriander cultivation in such a way that it does not pose any threat to human health in terms of the accumulation of heavy metals in the plant.

Conclusions

Understanding the accumulation of heavy metals in plant tissues is critical to address environmental and food safety concerns. By comparing the concentration of heavy metals in plant tissues with permissible levels, potential risks can be identified and strategies can be developed to minimize the impact of heavy metals pollution. This research is important and necessary to maintain the health of the ecosystem and human beings in the face of increasing demand for the use of non-conventional water in arid and semi-arid regions due to successive droughts and water resources crises. In this research, the concentrations of heavy metals in plant tissues were found to be non-hazardous to human health. However, regularly measurement of heavy metals in the effluent and within the plant tissues should not be stopped.