Abstract
The global increase in the human population and industrialisation has led to a rapid
increase in the generation of waste. Consequently, waste management gradually
becomes a major challenge for many countries internationally. Currently, disposal of
waste is a main waste management technique in South Africa. Various forms of waste
have the potential of causing detrimental effects on the environment and consequently
on humans. Thus, eco-toxicological assessment of waste before disposal is of
paramount importance.
Focus has been placed mainly on chemical analysis when it comes to the toxicological
risk assessment of waste. The chemical analysis does not provide information about
the potential synergistic, additive, or antagonistic effects of contaminants in the
environment.
Biological bioassays have the potential of reflecting the eco-toxicological danger of the
presence of contaminants or a mixture of contaminants in the environment. They also
have the potential of demonstrating the bioavailability of contaminants to biota.
It is thus vital to integrate physicochemical and biological analysis to identify possible
hazardous risks of waste to the environment. In this study, a multidisciplinary approach
including the physicochemical analysis and the Phytotoxkit bioassay was applied to
evaluate the potential toxicity of solid waste from the mining and power generating
industries. Leachate extractions of waste of concern was also evaluated using
standard toxicity tests.
Chrome solid waste, Coal solid waste A, and Clinker ash were identified as samples
of concern based on the phytotoxic effects expressed by the Phytotoxkit. These
samples showed high phytotoxic effects on the plants compared to Coal solid waste
B and Platinum tailings.
The toxicity of these samples was mainly attributed to the chemical content of the
samples. There was a possible combination of electrical conductivity and the chemical
content on the phytotoxicity of Coal solid waste A and Clinker ash. The low pH of Coal
solid waste A may have increased the solubility of a high concentration of elements
x
which possibly increased the electrical conductivity noted for this sample and
consequently toxicity to the plants.
The results of this study demonstrated that the Phytotoxkit can express the potential
effects of a combination of waste parameters on biota. The whole effluent toxicity
testing results showed that the three samples of concern pose a low hazard risk to the
aquatic environment from a leachate perspective.
From the results obtained in this study, it was concluded that supplementing chemical
analysis with the Phytotoxkit may aid in providing a comprehensive understanding of
the potential effects of the waste on the environment and subsequently determining
the appropriate waste management measures. It is therefore recommended to include
the Phytotoxkit bioassays during the eco-toxicological assessment of waste. Relevant
waste management structures in the country should consider revising the current
leachable threshold limits for some elements to ensure that plants are protected. This
increases the potential of repurposing the waste as recommended by the waste
hierarchy.
The information generated in this study and further research on the eco-toxicological
assessment of waste may aid in understanding the interaction of different parameters
of the waste and its potential hazard risk to the environment. This may increase
accuracy in identifying waste samples of concern and increase confidence in
determining the appropriate waste management measures for specific waste samples.