Soil Nematodes as Indicators of Heavy Metal Pollution: A Meta-Analysis

Camille Chauvin,David Makowski,Cécile Villenave,Anne Jimenez,Manon Trambolho,Hélène Cérémonie,Mickael Hedde

doi:10.4236/ojss.2020.1012028

Abstract

Nematodes have been used as bioindicators of soil quality for more than 20 years, and have been shown to have good potential for assessing the impact of heavy metal pollution on soil. They provide information about the biological condition of soil and can reveal dysfunctions linked to the presence of contaminants. In the case of contamination by multiple pollutants, bioindicators can reveal synergistic toxic effects (or “cocktail effects”) on organisms living in soil. These impacts are not revealed by the individual measurement of each pollutant. As the effects of heavy metals on nematode communities are not fully known, identifying reliable nematode-based parameters is not straightforward. Currently, knowledge gaps limit the operational use of these types of indices by soil managers. In this study, we performed a meta-analysis on the results of 37 studies from different countries to reveal general trends regarding the effect of multiple types of heavy metal pollution on soil nematode communities and indices. Based on the contamination level of each metal and using known toxicological threshold values, we defined four contamination classes to categorize soil polluted by heavy metals: normal concentration (c0), low contamination (c1), high contamination (c2), and very high (c3) contamination. The most sensitive nematode parameters, showing a strong relationship with the level of soil pollution, were the structure footprint, community footprint, abundance per trophic group (plant feeders, bacterial feeders and omnivores/predators) and taxonomic richness: all these parameters decreased with increased contamination. Our findings showed that fungal-feeding nematodes were relatively insensitive to metal contamination of soil and actually had a higher abundance in the very high contamination class (c3).

Highlights

Anthropogenic pollution, including heavy metal pollution, can pose a severe threat to humans and the environment ([1] [2])
In the meta-analysis, we summarized the currently available literature on soil polluted by heavy metals and the responses of soil nematodes with the aim of: 1) measuring the responses of nematode communities to heavy metal pollution, 2) testing if the proposed classification of four levels of contamination by multiple heavy metals is relevant to the global response of nematodes to soil pollution, and 3) identifying the most sensitive nematode parameters for use by soil managers
The datasets for c0, c1, c2 and c3 respectively contained 54, 53, 107 and 41 units of data, meaning that c0, c1 and c3 had a similar quantity of data, whereas about twice as much data was available for c2

Summary

Introduction

Anthropogenic pollution, including heavy metal pollution, can pose a severe threat to humans and the environment ([1] [2]). Identifying the effects of soil pollution on soil biodiversity is essential to better understand the impact of human activity on ecosystem functioning [5] [6] [7], allowing the development of effective management strategies for polluted soils [8] [9] and ensuring a more sustainable use of this important resource. A combination of the cp scale and feeding habits are used to define functional guilds as proposed by Bongers and Bongers [13]. Indices based on these characteristics can be used to analyse nematode community structure [21] [22] and any changes due to environmental disturbance [23] [24]

Objectives

Methods

Results

Discussion

Conclusion