Occurrence and ecological risk assessment of heavy metals in agricultural soils of Lake Chilwa catchment in Malawi, Sout
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Occurrence and ecological risk assessment of heavy metals in agricultural soils of Lake Chilwa catchment in Malawi, Southern Africa Chisomo Mussa1 · Timothy Biswick2 · Wisdom Changadeya4 · Harold Wilson Mapoma3 · Annett Junginger5 Received: 7 May 2020 / Accepted: 14 October 2020 © Springer Nature Switzerland AG 2020
Abstract Understanding the levels and associated ecological risk caused by heavy metals is important for the sustainable management and utilization of Lake Chilwa catchment, an important ecosystem in Malawi providing fertile lands for agriculture and a designated wetland ratified by the Ramsar convention in 1997. Concentrations of chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), arsenic (As), mercury (Hg) and cadmium (Cd) were analyzed from 22 soil sampling locations. Extraction and quantification were achieved by microwave digestion and Inductively Coupled Plasma Optical Emission Spectrometer, respectively. Mean values were detected in the following order; Zn > Cr > Ni > Cu > Pb > As. Strong correlations were observed between As and Pb (r = 0.85), Cr and Ni (r = 0.82), Cu and Ni (r = 0.81), Cr and Cu (r = 0.8), and Pb and Zn (r = 0.73) suggesting similar sources of input. Principal component analysis revealed that Cu, Pb, Zn and As originate from anthropogenic activities, while Cr and Ni were geogenic. The ecological risk caused by these metals, calculated by the Ecological Risk Index (RI) method, showed a low to moderate ecological risk. The wetland areas had higher overall concentrations and RI values compared to the rest of the catchment. It is therefore important to enforce measures to manage and control these levels to avoid their damaging effects. Keywords Heavy metals · Soil pollution · Ecological risk · Soil · Lake Chilwa catchment · Malawi
1 Introduction Soil pollution by heavy metals is an important environmental concern causing grave and irreparable damage to ecosystems. Rapid population growth, high urbanization rates, poor planning of cities, poor agricultural practices and lack of enforcement of environmental laws and regulations, among others, have been consistently associated with the accumulation of heavy metals in soils [1, 2]. Studies have been carried out to understand the levels of the metals in agricultural soils within the African continent.
Elevated levels of Cd, Cr, Cu, Ni, Pb and Zn in agricultural soils have been reported in Egypt [3], Nigeria [4], Kenya [5, 6], South Africa [7] and Zambia [8]. The concentrations were mainly attributed to mining activities, waste disposal, application of organic manure, inorganic fertilizers, herbicides and pesticides. Heavy metals accumulate in surface soils and migrate to crops by plant root respiration. Humans and animals are exposed directly or indirectly through consumption of contaminated food plants [9, 10]. Some metals such as Zn and Ni are essential for cell metabolic processes and are required within specified
* Chisomo Mussa, [email protected] | 1Department of Environmental Science and Management, Faculty o
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