Industrialization and heavy metals: Impacts on earthworm biodiversity and soil health

Introduction

Soils are dynamic ecosystems that sustain terrestrial life by regulating nutrient cycling, organic matter decomposition, and fertility. Among soil macro fauna, earthworms are widely recognized as ecosystem engineers due to their ability to restructure soil, enhance microbial activity, and regulate nutrient dynamics (Phillips et al., 2021) [10] . India, with its diverse agro climatic zones, harbors significant earthworm diversity, yet industrialization and land use change have increasingly disrupted their populations (Bharti et al., 2024; Chakraborty et al., 2023) [1,2] . Industrial expansion alters soil physicochemical properties through contamination, compaction, and reduced organic matter, leading to biodiversity decline. Comparative studies consistently show that earthworm abundance, biomass, and diversity indices are higher in non-industrial soils than in industrial soils, underscoring their sensitivity to anthropogenic stressors (Verma et al., 2021) [19] . Heavy metals such as cadmium, lead, and mercury accumulate in soils through industrial discharge and bioaccumulation in earthworm tissues, impairing growth, reproduction, and survival (Vaidya, 2022; Latifi et al., 2020) [17,9] . These toxic effects compromise their ecological functions, including litter decomposition, nutrient mineralization, and soil fertility enhancement (Raj et al., 2025) [11] . Ecologically, earthworms are classified into epigeic, endogeic, and anecic groups, each contributing uniquely to soil processes. Their burrowing and feeding activities improve aeration, water infiltration, and nutrient translocation, while their interactions with microbial communities accelerate carbon and nitrogen cycling (Gupta and Kumar, 2024; Goswami, 2025) [5,4] . Recent advances highlight earthworm microbiome interactions as next generation bioindicators of soil health, offering insights into pollutant detoxification and ecosystem resilience (Goswami, 2025) [4] . The climate change and industrial pollution act synergistically, reshaping earthworm community composition and ecological roles. Studies reveal that altered temperature and moisture regimes combined with contamination, significantly affect diversity indices and distribution patterns (Singh et al., 2020; Kooch, 2024) [13,8] . These findings emphasize the need for comparative assessments of industrial and non-industrial soils, particularly in regions like Rewari, Haryana, where rapid industrialization coexists with traditional agriculture.

Review of

Soil Biodiversity and Role of Earthworms

Soil represents one of the most biologically diverse ecosystems, supporting a vast array of microorganisms and macrofauna that collectively regulate nutrient cycling, organic matter decomposition, and fertility. Among these organisms, earthworms are widely recognized as ecosystem engineers, owing to their capacity to restructure soil, enhance microbial activity, and improve nutrient availability (Phillips et al., 2021) [10] . Their burrowing and casting activities increase aeration, water infiltration, and soil aggregation, thereby creating favorable conditions for plant growth and sustaining agricultural productivity (Torppa et al., 2024) [16] . India, with its varied agro climatic zones, harbors rich earthworm diversity, much of which is native and adapted to specific soil and climatic conditions (Bharti et al., 2024) [1] . However, rapid industrialization and land use changes have significantly altered soil properties, leading to biodiversity decline and reduced earthworm abundance (Verma et al., 2021) [19] . Heavy metals and pollutants introduced through industrial discharge accumulate in soils, bioaccumulation in earthworm tissues, and impair their growth, reproduction, and ecological functions (Yadav et al., 2023) [20] . Beyond their ecological roles, earthworms serve as bioindicators of soil health, reflecting changes in physicochemical parameters such as pH, moisture, and organic matter content (Gupta and Kumar, 2024) [5] . Their sensitivity to environmental stressors makes them valuable for monitoring ecosystem sustainability and assessing the impacts of industrialization on soil biodiversity. Recent advances highlight earthworm microbiome interactions and climate change studies as emerging areas of research, further underscoring their importance in ecological monitoring and sustainable soil management (Goswami, 2025) [4] . [12,7] . Recent surveys highlight that India harbors more than 400 species, of which nearly 89% are native, underscoring the country's role as a biodiversity hotspot (Bharti et al., 2024) [1] . Comparative studies reveal that regions such as the Western Ghats and Eastern Himalayas exhibit high species richness, while semi-arid zones like Gujarat Plains and the Trans Gangetic region show relatively poor diversity due to climatic constraints and anthropogenic pressures (Suthar, 2011;Singh et al., 2020) 13] . In Haryana, patchy distribution of endemic species such as Aporrectodea robustus and Octochaetus beatrix has been documented, reflecting the sensitivity of earthworm communities to soil physicochemical variations and industrial activity (Sharma and Poonam, 2014) [12] . 2025 [13,11] Earthworm diversity is also regulated by land use intensity.

Agricultural soils with moderate organic matter support higher abundance compared to heavily industrialized soils, where contamination and compaction reduce species richness (Verma et al., 2021) [19] . Recent findings emphasize that soil moisture, fertility, and organic carbon are the strongest drivers of diversity indices across agro ecosystems (Torppa et al., 2024) [16] . Moreover, climate change is reshaping distribution patterns, with altered rainfall and temperature regimes influencing population dynamics and community composition (Singh et al., 2020) [13] . The diversity of earthworms across India's agro climatic zones reflects a complex interplay of ecological, climatic, and anthropogenic factors. Understanding these patterns is essential for biodiversity conservation, sustainable agriculture, and ecological monitoring in rapidly industrializing regions such as Haryana.

Functional Roles of Earthworms in Soil Ecosystems

Earthworms are integral components of terrestrial ecosystems, often referred to as ecosystem engineers due to their ability to modify soil structure, enhance nutrient cycling, and regulate microbial activity (Phillips et al., 2021) [10] . Their burrowing and casting activities improve soil aeration, water infiltration, and aggregation, thereby creating favorable conditions for plant root growth and sustaining agricultural productivity (Torppa et al., 2024) [16] . Functionally, earthworms are classified into three ecological groups: epigeic species, which inhabit surface litter and accelerate organic matter decomposition; anecic species, which construct vertical burrows and incorporate surface residues into deeper layers; and endogeic species, which burrow horizontally and feed within the mineral soil, contributing to rhizosphere nutrient dynamics (Hendrix and Bohlen, 2002) [6] . Together, these groups maintain soil fertility and resilience across diverse agro ecosystems. Earthworms also play a pivotal role in nutrient mineralization and cycling. By ingesting organic debris with varying carbon to nitrogen ratios, they convert it into nutrient rich casts that enhance nitrogen and phosphorus availability for plants (Gupta and Kumar, 2024) [5] . Their interactions with soil microbes further accelerate decomposition processes, supporting carbon sequestration and improving soil health (Goswami, 2025) [4] . Meta analyses confirm that earthworm activity significantly increases crop yields, highlighting their agronomic importance (Van Groenigen et al., 2014) [18] . Beyond soil fertility, earthworms act as bioindicators of environmental quality. Their sensitivity to pollutants such as heavy metals and micro plastics makes them valuable for monitoring soil contamination and ecosystem sustainability (Yadav et al., 2023; Fan et al., 2023) [20,3] . Recent studies emphasize that earthworm microbiome interactions provide novel insights into pollutant detoxification and resilience mechanisms, positioning them as next generation indicators of soil health (Goswami, 2025) [4] . The functional roles of earthworms extend beyond decomposition and nutrient cycling to encompass ecological monitoring, sustainable agriculture, and climate resilience. Their contributions underscore the need to conserve earthworm diversity, particularly in regions undergoing rapid industrialization and land use change.

Industrialization, Heavy Metal Contamination, and Earthworm

Communities: Industrialization has profoundly altered soil ecosystems by introducing pollutants, modifying land cover, and disrupting natural biodiversity. Among soil fauna, earthworms are particularly sensitive to industrial stressors, making them reliable indicators of soil health (Verma et al., 2021) [19] . Industrial soils often exhibit reduced abundance, biomass, and diversity compared to non-industrial soils, reflecting the negative impacts of contamination, compaction, and reduced organic matter (Singh et al., 2020) [13] . One of the most critical consequences of industrial activity is the accumulation of heavy metals such as cadmium, lead, chromium, and mercury in soils. These metals enter earthworm tissues through ingestion of contaminated organic matter or dermal absorption, leading to physiological stress, reduced growth, impaired reproduction, and histological damage (Yadav et al., 2023) [20] . Recent studies confirm that heavy metal bioaccumulation can disrupt DNA integrity, enzyme activity, and metabolic pathways, thereby compromising earthworm survival and ecological functions (Latifi et al., 2020; Vaidya, 2022) [9,17] . The ecological implications extend beyond earthworm populations. By reducing their ability to decompose organic matter and recycle nutrients, heavy metal contamination diminishes soil fertility and plant productivity (Raj et al., 2025) [11] . Furthermore, synergistic effects of industrial pollution and climate change exacerbate stress on earthworm communities, altering diversity indices and distribution patterns across agro ecosystems (Singh et al., 2020; Kooch, 2024) [13,8] . Despite these challenges, earthworms continue to play a role in bioremediation. Their interactions with soil microbes can enhance pollutant degradation and nutrient cycling, offering potential strategies for restoring contaminated soils (Gupta and Kumar, 2024) [5] . Thus, comparative assessments of industrial and non-industrial soils are essential for understanding the extent of biodiversity loss, guiding remediation efforts, and ensuring sustainable soil management in rapidly industrializing regions such as Haryana. 2023) [20] Lead (Pb) [9] Chromium (Cr) [17] Mercury (Hg) Industrial effluents, mining

Oxidative stress markers, metabolic assays

Disruption of metabolic pathways, oxidative stress

Long-term soil contamination, reduced microbial activity Bioremediation using microbes and organic matter (Yadav et al., 2023) [20] [13,11] Bioindicator role

Sensitivity to pollutants and soil changes

Laboratory bioassays, ecological monitoring

Physiological and reproductive endpoints reveal contamination

Early detection of soil stress and contamination

Use earthworms in biomonitoring frameworks (Gupta and Kumar, 2024) [5] 2.5 Earthworms as Bioindicators of Soil Health and Environmental Quality Earthworms are increasingly recognized as bioindicators of soil health, owing to their sensitivity to changes in physicochemical properties and their ability to reflect ecosystem quality. Their abundance, diversity, and community structure provide valuable insights into soil fertility, contamination levels, and ecological resilience (Singh et al., 2020) [13] . Because they interact directly with soil through feeding, burrowing, and casting, earthworms integrate multiple environmental signals, making them reliable indicators of both natural and anthropogenic disturbances (Verma et al., 2021) [19] . Industrial and agricultural activities often introduce pollutants such as heavy metals, pesticides, and micro plastics into soils. Earthworm's bioaccumulation these contaminants and their physiological, histological, and reproductive responses serve as measurable endpoints for environmental monitoring et al., 2023; Fan et al., 2023) [20,3] . For example, reduced cocoon production, altered enzyme activity, and tissue damage have been documented in contaminated soils, highlighting their role as early warning systems for ecological stress (Latifi et al., 2020) [9] . Beyond contamination, earthworm diversity indices are strongly correlated with soil properties such as moisture, organic carbon, and pH. Studies demonstrate that soils with higher fertility and balanced moisture regimes support greater earthworm abundance and species richness, whereas degraded or polluted soils show reduced diversity (Torppa et al., 2024) [16] . This relationship underscores their utility in assessing soil quality across different land use systems. Recent advances emphasize the importance of earthworm microbiome interactions as next generation bioindicators. The gut microbial communities of earthworms respond dynamically to pollutants and soil conditions, offering new avenues for monitoring ecosystem health (Goswami, 2025) [4] . Together, these findings establish earthworms not only as contributors to soil fertility but also as critical tools for evaluating environmental quality in the face of industrialization and climate change.

Comparative Assessment of Industrial and Non Industrial Soils in Rewari District

The district of Rewari in Haryana represents a unique landscape where rapid industrial expansion coexists with traditional agricultural practices. This juxtaposition provides an ideal setting for comparative studies of soil biodiversity, particularly earthworm communities. Industrial soils, often exposed to heavy metal contamination, reduced organic matter, and altered physicochemical properties, contrast sharply with non-industrial soils such as agricultural fields and horticultural gardens that maintain relatively stable ecological conditions (Verma et al., 2021) [19] . Recent studies demonstrate that earthworm abundance, biomass, and diversity indices are consistently higher in non industrial soils compared to industrial sites (Singh et al., 2020) [13] . Industrial soils typically exhibit lower species richness and evenness due to contamination and compaction, while non-industrial soils support diverse communities that contribute to nutrient cycling and soil fertility (Torppa et al., 2024) [16] . Heavy metals such as cadmium, lead, and chromium, prevalent in industrial soils, bioaccumulation in earthworm tissues, impairing their physiological functions and reducing reproductive success (Yadav et al., 2023; Latifi et al., 2020) [20,9] . Comparative assessments in Rewari are particularly significant because they highlight the ecological costs of industrialization in a region undergoing rapid economic development. By analyzing soil parameters such as pH, organic matter, moisture, and nutrient availability alongside earthworm diversity indices, researchers can establish clear correlations between environmental stressors and biodiversity decline (Gupta and Kumar, 2024) [5] . These findings not only provide insights into the resilience of earthworm communities but also underscore their role as bioindicators of soil health. Ultimately, such comparative studies contribute to sustainable land use planning and environmental management. They emphasize the need for remediation strategies, including organic amendments and bioremediation approaches, to restore soil quality in industrial zones while safeguarding biodiversity in non industrial landscapes (Raj et al., 2025) [11] .

Conclusion

The review highlights the pivotal role of earthworms as ecosystem engineers and bioindicators of soil health, emphasizing their contributions to nutrient cycling, organic matter decomposition, and fertility across India's diverse agro climatic zones. Evidence consistently demonstrates that industrialization and heavy metal contamination reduce earthworm abundance, biomass, and diversity, thereby impairing ecological functions and diminishing soil quality. Comparative studies, particularly in Rewari district, reveal stark contrasts between industrial and non-industrial soils, underscoring the ecological costs of rapid industrial expansion. Functional classifications of earthworm's epigeic, endogeic, and anecic illustrate their unique contributions to soil processes, while emerging research on microbiome interactions and climate change impacts expands their relevance as next generation bioindicators. Collectively, these findings establish earthworms as critical tools for monitoring environmental quality, guiding remediation strategies, and ensuring sustainable soil management. The synthesis underscores the urgent need for integrated approaches that combine biodiversity conservation, pollution control, and adaptive land use planning to safeguard soil ecosystems in industrializing regions.

CRediT authorship contribution statement

• Anoop: Writing -original draft, Validation, Formal analysis, Data curation, Conceptualization.

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