It is well established that earthworms and their products promote plant growth and improve crop yield, but more information about their mechanisms of action, especially at cellular level, is required. This study assessed the enzyme and bacterial activities of vermifluid secreted by a tropical wetland earthworm, Alma millsoni. The effects of the vermifluid on the mitotic activities and root growth of Allium cepa (onions) were evaluated. Vermifluid enzyme and bacterial activities were assessed using standard procedures. Mitotic activities were evaluated using the Allium assay squash technique. Root lengths in onions grown in graduated dilutions of vermifluid were measured using a metre rule. Phosphatase had the highest activity (39.00 ± 3.70 units/ml/min) in the vermifluid, followed by urease (4.90 ± 0.18 units/ml/min), protease (3.20 ± 0.28 units/ml/min), amylase (1.40 ± 0.09 units/ml/min) and lipase (0.001 ± 0.00 units/ml/min). The total microbial count (TBC) and total fungi count (TFC) in the vermifluid were 6.0 × 104 CFU/ml and 2.4 × 105 CFU/ml, respectively. Results also indicated that the lower the vermifluid concentrations, the higher the number of dividing cells and mitotic index in onion roots. Onion roots grown in 10% vermifluid had the highest significant (P < 0.05) root growth of 2.65 ± 0.30 cm, 4.01 ± 0.61 cm, and 4.54 ± 0.62 cm, at 12-hour, 24-hour, and 72-hour exposure period, respectively. The inverse relationships between onion mitotic activities, root growth and vermifluid concentrations imply that the growth-promoting enzymes and other products in vermifluid stimulate cellular root growth better in small concentrations. Keywords: Alma millsoni, earthworm fluid, enzymes, microbial activities, mitosis, phosphatase.

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.

No abstract

No abstract