Potential of Cassia alata and Cassia multijuga to phytoremediate mined-out soils in the Puruni Mining Area

Quincy Thom & Patrick Ketwaru

Published: October 5, 2021 • Book of Abstracts – Student Research, Volume 2

Quincy Thom ✉️ Department of Environmental Studies. Faculty of Earth and Environmental Sciences. University of Guyana – Turkeyen Campus. Greater Georgetown, Guyana.

Patrick Ketwaru Department of Chemistry. Faculty of Natural Sciences. University of Guyana –Turkeyen Campus. Greater Georgetown, Guyana.

Phytoremediation is a technology that uses plants to remove contaminants such as mercury from soil. This research examined phytoremediation as an option to remove mercury from mined out soils in the Puruni mining area, Mazaruni (Region VII). The study examined the phytoextractive capabilities of the Cassia alata (Carrion Crow Bush) and Cassia multijuga (False Sicklepod). Soil sampling was conducted to determine mercury levels at five mined out sites: Jubilee Creek Nos. 1 & 2, Chinese Creek, Tiger Creek, and the Takatu area. A tube auger and sieve were used to extract soil samples and remove debris. Soil pH levels were tested in-situ using a Hach Sension pH meter. Mercury levels in the soil and in naturally growing C. alata and C. multijuga sampled from the mined-out sites were analysed at an accredited laboratory using the Cold Vapour Absorption Spectroscopy (CVAAS) method. To determine mercury uptake, two field plots, each planted with ten C. alata seedlings, were established at Chinese Creek and Jubilee Creek No. 1. A control plot with five C. alata seedlings was also established in Georgetown using sterilised (mercury-free) soil. Seedlings from the field and control plots were randomly harvested and analysed for mercury using the CVAAS method. The results indicated that mercury was present in 48% of soil samples taken from the five sites, with levels ranging from 3 ng/g at Tiger Creek to 140 ng/g at Jubilee Creek. Sites with lower soil pH values recorded the highest levels of mercury. In naturally growing C. alata, the highest mercury level recorded was 160 ng/g in the leaves and stems and 47 ng/g in the roots, while in naturally occurring C. multijuga, the highest mercury level was 87 ng/g in the leaves and stems and 1,210 ng/g in the roots. All C. alata (100%) samples harvested from the control plot recorded a zero (0) value for mercury. Analysis of C. alata harvested at the field plots confirmed that all samples showed traces of mercury uptake, ranging from 2 ng/g at Chinese Creek to 200 ng/g at Jubilee Creek No. 1. The research demonstrated that C. alata can extract mercury from mined out soils without the addition of ligands or other chemicals to promote absorption. It also highlights the potential of C. multijuga as a possible alternative species for phytoremediation.


Keywords: Phytoremediation; Cassia alata; Cassia multijuga; mined-out soils


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Published: 2021-10-05