Abstract
Background.In addition to improving soil fertility and crop production, earthworms have been found to be useful in the removal of contaminants from soil, known as vermiremediation. Previous studies on vermiremediation have focused primarily on organic wastes, with relatively less attention paid to inorganic contaminants. In addition, some basic terms used in environmental health studies have often not been properly clarified.Objectives.The present study is a review of the state of the literature on the effectiveness of using earthworms to remediate organic and inorganic (metal) soil contaminants. Earthworms’ actions in remediation of organic and inorganic contaminants are described. Some terms that are used interchangeably in environmental health are clarified. The challenges and limitations of vermiremediation are highlighted.Methods.A systematic literature search was conducted to access online academic publications indexed in Google Scholar, PubMed, Scopus, Clarivate Analytics (Web of Science), ScienceDirect, ResearchGate and Springer Link. A total of 165 publications on the subject matter were accessed, out of which 47 were used for the review.Discussion.Empirical and theoretical information from the literature showed evidence of the significant contributions of earthworms to the removal of soil organic contaminants and metals. Earthworms indirectly facilitate the conversion of organic contaminants by promoting microbial and enzyme activities. Some organic contaminants are directly taken up through dermal and intestinal absorption and accumulated by preferential sequestration in sub-organismic and tissue fractions of earthworms. Metals are directly removed and accumulated by the mechanism of detoxification and sequestration, via metallothioneins induction. The terms ‘contaminants’ and ‘pollutants’ have different meanings and should not be used interchangeably. Although vermiremediation presents an ideal clean-up technique, it is limited in application to only mildly contaminated soil environments. Ethical concerns should not pose a serious issue because vermiremediation simply takes advantage of earthworms’ natural soil-conditioning abilities. Many vermiremediation processes, especially of organic wastes, are harmless to earthworms, improving the soil for their growth and survival.Conclusions.Vermiremediation presents a good long-term biological option to clean up mildly contaminated soil. It may be deployed as a secondary measure to rid the soil of residual contaminants after applying physicochemical remediation techniques to an overtly polluted soil environment.Competing Interests.The authors declare no competing financial interests.
Highlights
Earthworms promote plant growth and productivity through complex mechanical and biochemical interactions with soil abiotic and biotic components.[1]
The words, terms, clauses, and phrases used in the literature search included biological remediation, bioremediation, vermiremediation, use of earthworms in remediation, vermiremediation of organic contaminants, vermiremediation of inorganic contaminants, vermiremediation of metals, pollution and contamination, pollutants and contaminants, and metallothioneins
Of the 47 academic articles included in the present review, only four attempted to define or clarify some basic terms used in environmental health ‘pollution’, ‘pollutants’, ‘contamination’, and ‘contaminants’
Summary
Earthworms promote plant growth and productivity through complex mechanical and biochemical interactions with soil abiotic and biotic components.[1]. The present study is a review of the state of the literature on the effectiveness of using earthworms to remediate organic and inorganic (metal) soil contaminants. Vermiremediation presents an ideal clean-up technique, it is limited in application to only mildly contaminated soil environments. Vermiremediation presents a good long-term biological option to clean up mildly contaminated soil. It may be deployed as a secondary measure to rid the soil of residual contaminants after applying physicochemical remediation techniques to an overtly polluted soil environment. The guts of earthworms are host to millions of enzymes and microorganisms which facilitate the rapid biochemical conversion and mineralization of soil organic matters, thereby enriching soil.[1] All these processes, together with other factors, facilitate increased plant growth and crop yield
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