Comparison of mercury and methylmercury bioaccumulation in earthworms (<i>Bimastus parvus</i>) native to landfill-leachate-contaminated forest soil

Abstract

Total mercury (THg) and methylmercury (MeHg) bioaccumulation was explored in the Bimastus parvus species of earthworm (B. parvus) native to the leachate-contaminated forest soils around a Hg-polluted traditional landfill in Japan. General soil properties and concentrations of THg and MeHg in forest soils and in B. parvus were determined. The results indicated that the average THg concentrations in B. parvus and in forest soils in the leachate-contaminated sites were 10.21 and 14.90 times higher than those in the reference sites, respectively, whereas similar average MeHg concentrations were observed in forest soils (< 0.01 mg kg) and in B. parvus (0.100-0.114 mg kg) across all sampled sites. The average bioaccumulation factors of THg in B. parvus (BAF) in forest soil were similar between the leachate-contaminated sites and the reference sites. Cluster and regression analyses demonstrated that the B. parvus Hg (THg and MeHg) and soil THg were positively correlated with each other and with soil organic matter (SOM) and clays, but were negatively correlated with sand and hardly correlated with silts and pH in leachate-contaminated forest soils. From these results, it was proposed that Hg exposure to food chains is possible through B. parvus, because B. parvus showed a high ability to accumulate THg and MeHg in both leachate-contaminated and reference forest soils. Together, these findings indicated that the role of B. parvus in MeHg production is not clear, and it is possible that the MeHg in B. parvus was firstly formed within forest soils and then accumulated in their tissues.

Soil Bioavailability and Native Plant Uptake of Mercury in the Contaminated Sites at Kodaikanal, India

“…The pH of the soil samples ranged from 4.14 to 6.16, 3.26 to 4.68, 4.27 to 6.32 and 3.38 to 4.64 in D1, D2, D3 and D4, respectively. Similar results were recorded by He et al [13] with pH ranged from 4.08 to 5.67 in forest soils. Low soil pH promotes metal solubility and their availability to plants which emphasizes it as an important factor in metal uptake [14,15].…”

“…The total mercury of the samples ranged from 0.24 to 3.80, 0.84 to 1.55, 0.45 to 1.67 and 0.19 to 4.97 mg kg -1 in D1, D2, D3 and D4, respectively whereas the water soluble mercury fraction ranged from 0.01 to 0.07 and 0.01 to 0.04 mg kg -1 in D1 and D4, respectively corresponding to 0.5 to 5.36 % of the total. These results were correlated with the findings of He et al [13] and Rieder et al [21]. The soil mercury content recorded was less than the prescribed permissible limit by Canadian Soil Quality Guidelines which holds 6.6 mg kg -1 for residential as well as agricultural area and 50 mg kg -1 for industrial area [22].…”

Soil Hg Contamination Impact on Earthworms’ Gut Microbiome

“…The direct impact of Hg on the earthworms' biomass might have been outweighed by the rich soil quality in experiment 1 and the poor quality in experiment 2. However, the accumulation of both THg and MeHg in the earthworms compared with in the soil matrix was considerable in both experiments, in line with observations from previous field studies of a correlation between Hg bioaccumulation and soil total Hg, organic matter and clay contents [23,27,48]. Furthermore, the Hg and MeHg bioaccumulation might have affected the earthworms over a longer period than the incubation duration, for example by impacting their burrowing behavior or respiration [49].…”

“…In this study, we demonstrated the impact of Hg contamination and accumulation in earthworms using long-term Hg-contaminated soils [24]. Whereas laboratory experiments using Hg-spiked soil often aim for concentrations of up to 500 mg kg −1 [4,47], the total Hg concentrations in our incubated soils (36 mg kg −1 ) were in the range of total Hg concentrations found in other Hg-polluted sites, such as in a leachate-contaminated soil (THg 1.3 µg g −1 dw, [48]) or a landfill (THg 0.9-97.5 µg g −1 , [23]).…”

Identification and Characterization of Peruvian Native Bacterial Strains as Bioremediation of Hg-Polluted Water and Soils Due to Artisanal and Small-Scale Gold Mining in the Secocha Annex, Arequipa

“…There are many studies of bacteria that show potential in the removal of Hg from contaminated water, however, in general terms, the bioremediation of soils contaminated by Hg has been little investigated [33,37,38]. Added to this is the use of native bacteria, as some microorganisms develop resistance to Hg contamination, making them promising natural candidates for bioremediation [39][40][41][42].…”