Soil contamination
Soil contamination refers to the introduction of harmful substances into soil through anthropogenic activities, altering its chemical, physical, or biological properties and rendering it unfit for ecological functions, agriculture, or human use.[1]
Primary contaminants include heavy metals like lead and cadmium, persistent organic pollutants such as pesticides and polychlorinated biphenyls, and petroleum hydrocarbons, originating from industrial discharges, agricultural applications, mining operations, and waste disposal practices.[2][3]
These substances can leach into groundwater, bioaccumulate in food chains, and cause adverse health effects in humans including carcinogenic risks and developmental disorders, while also diminishing soil fertility and biodiversity.[4][5]
Remediation strategies encompass physical methods like excavation and thermal treatment, biological approaches such as phytoremediation, and chemical techniques including oxidation, though their efficacy varies by contaminant type and site conditions, often requiring integrated applications to achieve restoration.[6][7]
Global assessments indicate that soil contamination affects millions of hectares, posing long-term challenges to food security and environmental sustainability, with ongoing debates over regulatory thresholds and the balance between economic development and ecological preservation.[8]
Definition and Fundamentals
Definition and Scope
Soil contamination denotes the introduction or accumulation of substances in soil at concentrations exceeding natural background levels, thereby impairing one or more soil functions, such as nutrient cycling, water retention, or support for biodiversity.[9] These substances, often including heavy metals like lead and cadmium, persistent organic pollutants such as polychlorinated biphenyls (PCBs), and petroleum hydrocarbons, originate predominantly from human activities and can persist due to soil's adsorptive properties.[10] Unlike transient pollutants, soil contaminants may bioaccumulate in organisms, transferring through food webs and posing risks to ecosystems and human health via direct dermal contact, inhalation of dust, incidental ingestion, or uptake into crops.[11] The scope of soil contamination encompasses both point sources, such as leaking underground storage tanks or industrial spills, and diffuse sources like atmospheric deposition from fossil fuel combustion or agricultural runoff carrying excess fertilizers and pesticides.[1] It is distinguished from natural soil variability, where trace elements occur geogenically without functional impairment; contamination requires demonstrable adverse effects, often quantified against site-specific or regulatory thresholds derived from toxicity data and exposure models.[12] Globally, this issue affects arable lands and urban areas, with implications for food security—as contaminated soils reduce crop yields and quality—and groundwater integrity, as leachates migrate downward.[13] Assessment of contamination's scope involves evaluating not only chemical concentrations but also bioavailability, which determines actual uptake risks, and long-term ecological resilience. Peer-reviewed studies emphasize that while some contaminants degrade via microbial activity or photolysis, many resist breakdown, necessitating remediation to restore soil utility.[10] Regulatory frameworks, such as those from the U.S. Environmental Protection Agency, define contamination based on risk-based corrective action levels tailored to land use, prioritizing protection of sensitive receptors like children or agricultural produce.[1] This delineation ensures that interventions target verifiable harms rather than mere presence of substances.Natural vs. Anthropogenic Sources
Soil contamination arises from both natural geological and biological processes and human activities, with the latter often amplifying concentrations beyond baseline levels in affected regions. Natural sources primarily involve geogenic processes, where parent bedrock weathers and releases trace elements such as arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc into the soil profile.[14] Volcanic eruptions and geothermal fluids contribute metals and sulfur compounds, as evidenced by elevated arsenic levels in soils near active volcanoes in regions like Iceland and Indonesia, where eruptions in 2010 deposited ash containing up to 200 mg/kg of arsenic.[15] Erosion and wildfires also mobilize naturally occurring contaminants; for instance, forest fires in California released mercury from soil organic matter, increasing concentrations by 20-50% in post-fire sediments as measured in 2018 studies.[11] These processes establish background levels, typically ranging from 0.1-10 mg/kg for most heavy metals in uncontaminated soils globally, varying by lithology—higher in areas with metal-rich rocks like black shales.[16] Anthropogenic sources dominate in industrialized and agricultural landscapes, introducing contaminants through direct deposition and indirect pathways like atmospheric transport. Industrial activities, including mining and smelting, account for localized hotspots; for example, lead concentrations in soils near smelters in China exceeded 1,000 mg/kg, far surpassing natural baselines of under 20 mg/kg, as documented in 2011 reviews of global sites.[17] Agricultural practices contribute via fertilizers, pesticides, and manure; phosphate fertilizers alone add cadmium at rates of 10-50 g/ha annually in intensive farming areas like Europe, accumulating to levels 2-5 times natural backgrounds over decades.[14] Urban and waste-related inputs, such as sewage sludge application and vehicle emissions, elevate polycyclic aromatic hydrocarbons (PAHs) and microplastics; global estimates indicate 14-17% of croplands polluted by toxic metals primarily from these sources, affecting 0.9-1.4 billion people via food chains.[14] Military activities and improper waste disposal further exacerbate issues, with unexploded ordnance leaching explosives like TNT into soils at concentrations up to 100 mg/kg in former battlefields.[11] Distinguishing natural from anthropogenic contributions requires geochemical tracers like enrichment factors and isotopic ratios, as human inputs often exceed geogenic baselines by orders of magnitude in populated areas—e.g., zinc levels in urban soils averaging 200-500 mg/kg versus 50-100 mg/kg naturally.[16] Empirical data show atmospheric deposition spreads anthropogenic pollutants to remote natural areas, mirroring urban contamination patterns globally; a 2023 analysis of 168 parks and adjacent forests found metal(loid)s, pesticides, and microplastics at comparable levels, indicating diffuse human influence overrides local geology in many cases.[4] While natural sources provide unavoidable baselines essential for risk assessment, anthropogenic dominance—responsible for 80-90% of exceedances in monitored agricultural soils—necessitates targeted remediation to prevent bioaccumulation and ecosystem disruption.[18] This interplay underscores that total contamination reflects both inherent soil chemistry and cumulative human pressures, with the latter driving most health and productivity risks.[14]Historical Development
Early Recognition and Industrial Era
Ancient civilizations, dating back to approximately 3000 BCE, demonstrated an empirical awareness of connections between soil quality, environmental factors, and human health, often linking poor soil conditions to disease prevalence without distinguishing contamination from natural degradation.[19] By the late 1700s and early 1800s, farmers in regions like the United States explicitly noted associations between specific soil properties—such as texture and nutrient content—and health outcomes, including susceptibility to illnesses, though systematic scientific documentation remained limited.[20] Pre-industrial contamination primarily stemmed from localized activities like ore smelting and mining, with historical soil profiles showing elevated lead (Pb) levels from ancient metallurgical processes, peaking during periods of intensified extraction as early as the Roman era.[21] These activities deposited heavy metals into soils, rendering adjacent lands infertile and affecting vegetation and water sources, though recognition was anecdotal and tied more to agricultural yield losses than explicit pollution awareness.[22] The Industrial Revolution, beginning in the mid-18th century in Britain and expanding across Europe and North America, markedly intensified soil contamination through widespread emissions of heavy metals, hydrocarbons, and industrial wastes from factories, coal combustion, and expanded mining operations.[23] By the mid-19th century, during the Second Industrial Revolution around 1850, anthropogenic lead contamination became globally detectable in soils, correlating with increased smelting and manufacturing scales that dispersed pollutants via atmospheric deposition and direct effluents.[24] Observations in industrial hubs, such as Manchester's factory districts, documented barren soils laden with ash and metals, prompting early regulatory responses like Britain's Alkali Acts of the 1860s, which indirectly addressed soil impacts by curbing gaseous emissions that precipitated contaminants.[25] These developments shifted recognition from sporadic local effects to a broader acknowledgment of systemic environmental alteration, though remediation efforts lagged behind pollution generation.Post-WWII Expansion and Awareness
Following World War II, economic reconstruction and industrial expansion in Europe and North America accelerated soil contamination through intensified manufacturing, urbanization, and agricultural practices. Chemical production, repurposed from wartime technologies, boomed; for instance, organochlorine pesticides like DDT, developed in the 1940s for vector control, saw agricultural applications surge globally, with U.S. usage alone reaching hundreds of thousands of tons annually by the 1950s, leading to persistent residues in topsoils that inhibited microbial activity and nutrient cycling.[26][27] Synthetic fertilizers, applied at rates exceeding 100 kg nitrogen per hectare in intensive farming regions by the late 1950s, contributed excess salts and heavy metals like cadmium from phosphate rock impurities, degrading soil structure and fertility over large areas.[28] Industrial effluents from steel mills, petrochemical plants, and battery manufacturing discharged arsenic, lead, and chromium into soils via unregulated dumping, with documented hotspots in river valleys where concentrations exceeded natural baselines by factors of 10–100.[29] Urban sprawl compounded these issues, as post-war housing booms in cities like those in the U.S. Rust Belt incorporated landfills and slag heaps from steel production, embedding polycyclic aromatic hydrocarbons (PAHs) and dioxins into subsurface soils at depths up to 2 meters.[30] Military surplus chemicals and unexploded ordnance from training sites further contaminated rural and peri-urban lands, with unexploded munitions leaching explosives like TNT into groundwater and soils across former battlefields and bases.[31] By the 1960s, agricultural intensification had distributed contaminants diffusely, with pesticide half-lives in soil ranging from months to years, facilitating bioaccumulation in food chains.[32] Public and scientific awareness of soil contamination crystallized in the 1960s amid broader environmental concerns over chemical persistence. Rachel Carson's 1962 publication Silent Spring detailed how pesticides like DDT accumulated in soils, disrupting earthworm populations and soil invertebrates essential for decomposition, while linking residues to bird eggshell thinning and potential human carcinogenicity through empirical field observations.[33][34] Early studies, such as those by the U.S. Public Health Service in the late 1950s, quantified pesticide residues in Midwestern farm soils at levels up to 10 ppm, prompting debates on long-term ecological risks despite industry claims of safety based on short-term efficacy data.[35] This growing recognition influenced policy, with the U.S. Congress passing the Water Quality Act of 1965, which indirectly addressed soil runoff into waterways, and culminating in the creation of the Environmental Protection Agency (EPA) in 1970 to oversee hazardous waste sites where soil pollution from post-war dumping was evident.[36] In Europe, the 1960s saw initial soil surveys by agencies like the UK's Agricultural Research Council revealing heavy metal elevations from sewage sludge application, fostering calls for remediation standards by the decade's end.[37] These developments marked a shift from viewing soil as an infinite sink for wastes to recognizing it as a finite resource vulnerable to irreversible degradation, though regulatory responses lagged behind contamination scales due to economic dependencies on chemical-intensive growth.Causes of Contamination
Industrial and Mining Activities
Industrial activities, particularly metal smelting, chemical manufacturing, and petrochemical processing, introduce heavy metals such as lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), chromium (Cr), copper (Cu), zinc (Zn), and nickel (Ni) into soils through direct discharges, spills, waste effluents, and atmospheric deposition from stack emissions.[38] [39] These contaminants persist due to low mobility and bioaccumulation potential, with soil concentrations in industrial zones often exceeding natural background levels by factors of 10 to 100; for instance, in South China's intense industrial areas, Pb levels reached up to 500 mg/kg in topsoils near factories, surpassing regulatory limits.[40] Organic pollutants like polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and solvents from oil refining and cleaning operations further contaminate soils via leaching from storage sites and accidental releases.[41] Mining operations exacerbate soil contamination primarily through the generation of tailings—finely ground rock residues containing residual heavy metals—and acid mine drainage (AMD), where exposure of sulfide minerals to air and water during extraction produces sulfuric acid that mobilizes metals like iron (Fe), manganese (Mn), Pb, Zn, and Cu into surrounding soils via runoff and infiltration.[42] [43] Tailings impoundments, often unstable, release contaminants; for example, gold mining tailings accumulate As, Pb, and Hg, with soil Pb concentrations near sites in low-grade copper sulfide mines averaging 200-500 mg/kg, posing ecological risks despite varying pollution indices.[44] [45] In regions like Yantai, China, mining and smelting have elevated soil Cd and Pb to 5-10 times background values, driven by ore processing emissions since the mid-20th century intensification.[46] Waste rock dumps and open-pit exposures contribute additional dust-borne metals, with global analyses indicating industrial-mining hotspots account for substantial shares of anthropogenic toxic metal inputs to the pedosphere.[14]Agricultural and Urban Practices
Agricultural practices introduce contaminants to soil through the application of synthetic fertilizers, pesticides, and organic amendments like animal manure and sewage sludge. Phosphate fertilizers, derived from rock phosphate, often contain trace heavy metals such as cadmium, which accumulate over repeated applications; studies indicate that cadmium levels in agricultural soils can exceed environmental quality standards in regions with intensive farming, impairing microbial activity and crop uptake.[47] Nitrogen and phosphorus from fertilizers contribute to eutrophication precursors in soil, while excess application leads to nitrate leaching and persistent residues that alter soil chemistry.[37] Pesticides, including herbicides like glyphosate and insecticides such as neonicotinoids, persist in soil for months to years, with organochlorine compounds like DDT leaving legacy contamination detectable decades after bans in many countries.[48] Livestock manure introduces antibiotics, hormones, and heavy metals like copper and zinc from feed additives, exacerbating antibiotic resistance in soil microbiomes.[49] Globally, heavy metal pollution affects 14 to 17% of cropland, with agricultural inputs identified as primary drivers alongside atmospheric deposition; this contamination threatens food security by facilitating uptake into edible crops, potentially exposing 0.9 to 1.4 billion people in affected regions.[14] Atmospheric deposition from fertilizer production and pesticide volatilization further amplifies metal accumulation, as evidenced in studies of cadmium, lead, copper, and zinc in vegetable-growing soils.[50] Urban practices contaminate soils via stormwater runoff from impervious surfaces like roads and rooftops, which mobilizes pollutants including heavy metals (e.g., lead, zinc from tire wear and brake dust), polycyclic aromatic hydrocarbons from vehicle exhaust, and oils.[51] De-icing salts introduce sodium and chloride, degrading soil structure and elevating salinity in roadside areas, while construction activities release sediments laden with metals and hydrocarbons.[52] Leaks from aging sewage infrastructure contribute fecal pathogens, pharmaceuticals, and nutrients, with urban stormwater often carrying human waste indicators at concentrations rivaling untreated effluents.[53] Municipal waste disposal, including land application of biosolids and informal dumps, adds organic micropollutants and metals, with erosion and flooding redistributing these to adjacent soils.[54] In urban gardens, legacy lead from historical paint and gasoline persists, posing ingestion risks despite remediation efforts.[55]Military and Waste Management
Military operations frequently result in soil contamination through the deposition of unexploded ordnance, residues from explosives, fuels, solvents, and firefighting agents. Key contaminants include volatile organic compounds such as trichloroethylene (TCE) and tetrachloroethylene (PCE), polychlorinated biphenyls (PCBs), heavy metals like lead and asbestos, nitroaromatic compounds from munitions, and per- and polyfluoroalkyl substances (PFAS) from aqueous film-forming foams (AFFF) used in fire suppression training.[56][57] These substances persist in soil due to low biodegradability and can migrate via leaching or erosion, affecting site usability and nearby ecosystems. The U.S. Department of Defense (DoD) oversees cleanup at over 770 contaminated installations, with munitions-related sites alone projected to cost between $8 billion and $35 billion for remediation as of 2025.[58][59] Specific examples illustrate the scale: At the former Loring Air Force Base in Maine, deactivated in 1994, Air Force activities contaminated soil and groundwater with chlorinated solvents, petroleum hydrocarbons, and other wastes, necessitating ongoing Superfund remediation.[60] The Alabama Army Ammunition Plant, operational from 1941 to 2010, left widespread soil pollution with nitroaromatic explosives byproducts, asbestos, and lead across production areas.[61] PFAS contamination is particularly pervasive, with documented exceedances at bases like Eielson Air Force Base in Alaska, where foam use during drills infiltrated soils and aquifers.[62] In conflict zones, such as Ukraine since 2022, explosions and vehicle combustion have elevated soil heavy metal levels, including lead, nickel, copper, and zinc, from fragmented munitions and debris.[63][64] Waste management practices contribute to soil contamination primarily through leachate generation in landfills and improper hazardous waste disposal. Leachate—liquid percolating through waste—carries dissolved organics, heavy metals (e.g., cadmium, lead), and nutrients, which breach liners or infiltrate unlined sites, altering soil pH, structure, and microbial communities.[1][65] Long-term studies near landfills document suppressed litter decomposition and root quality in adjacent soils, alongside elevated pollutant bioaccumulation that impairs agriculture and biodiversity.[65] In the U.S., thousands of legacy sites, including those under Superfund, stem from industrial waste dumping predating modern regulations like the Resource Conservation and Recovery Act of 1976.[1] Notable cases include open dumps and e-waste processing areas, where informal recycling releases dioxins, polycyclic aromatic hydrocarbons, and metals via burning and acid leaching. For instance, leachate from municipal solid waste landfills has been linked to groundwater-soil interfaces contaminated with ammonia, phenols, and pathogens, persisting for decades without engineered controls.[66] Hazardous waste mismanagement, such as unpermitted burial of solvents or pesticides, exacerbates point-source pollution, with EPA data indicating that landfill-adjacent soils often exceed safe thresholds for human contact or plant uptake.[1] Remediation challenges persist due to waste heterogeneity and volume, underscoring the causal link between inadequate containment and diffuse soil degradation.[66]Detection and Assessment
Sampling and Analytical Methods
Soil sampling for contamination assessment involves systematic collection of representative subsamples to characterize contaminant distribution, concentration, and extent across heterogeneous sites. Procedures prioritize avoiding cross-contamination by progressing from least to most suspected areas, using dedicated tools such as stainless steel augers, coring devices, or direct-push probes for subsurface access.[67] Sampling depths typically range from surface (0-15 cm) for urban or agricultural exposure risks to deeper profiles (up to several meters) for groundwater migration pathways, with vertical stratification to capture leaching gradients.[68] Grid-based systematic sampling, often on 10-50 meter intervals, ensures spatial coverage, while targeted "hot spot" delineation employs search sampling to refine boundaries where exceedances surpass regulatory thresholds like EPA soil screening levels.[69] Common techniques include discrete grab sampling for volatiles to minimize headspace loss, composite sampling by mixing multiple subsamples for cost-effective averaging, and incremental sampling methodology (ISM) per EPA guidelines, which homogenizes 30-100 increments per decision unit to reduce variability from soil heterogeneity.[70] For volatile organic compounds (VOCs), EPA Method 5035 mandates methanol preservation and coring to preserve integrity, with samples stored at 4°C and analyzed within 14 days.[71] Equipment decontamination between stations—using rinsates like 10% nitric acid followed by distilled water—prevents artifactual contamination, as verified by field blanks yielding <5% of reporting limits.[72] Chain-of-custody protocols and quality assurance/quality control (QA/QC) measures, including duplicates at 10% frequency, underpin data reliability.[73] Analytical methods quantify contaminants via standardized laboratory protocols under EPA SW-846, ensuring detection limits below risk-based thresholds. Metals like lead, cadmium, and arsenic are extracted via acid digestion (EPA 3050B) and quantified by inductively coupled plasma mass spectrometry (ICP-MS) or optical emission spectrometry (ICP-OES, Method 6010), achieving parts-per-billion sensitivity for bioavailable fractions.[74] Organic pollutants, including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), undergo solvent extraction followed by gas chromatography-mass spectrometry (GC-MS, Method 8270), with electron capture detection (GC-ECD) for halogenated compounds like pesticides.[75] Field-portable options, such as X-ray fluorescence (XRF) for in-situ metal screening or photoionization detectors (PIDs) for VOCs, provide rapid triage but require lab confirmation due to matrix interferences yielding 20-50% variability.[76] Data validation assesses precision (relative percent difference <30% for duplicates) and accuracy via matrix spikes, rejecting outliers exceeding control limits to support defensible risk assessments.[77]Risk Evaluation Frameworks
Risk evaluation frameworks for soil contamination systematically assess potential adverse effects on human health and ecosystems by integrating contaminant characteristics, exposure pathways, and dose-response data. These frameworks typically follow a tiered structure, beginning with conservative screening levels derived from generic assumptions about exposure and toxicity, progressing to site-specific modeling if initial thresholds are exceeded. The U.S. Environmental Protection Agency (EPA) employs such an approach in its Superfund Soil Screening Guidance, which calculates risk-based soil screening levels (SSLs) to determine if further investigation or remediation is warranted at contaminated sites.[78] This method prioritizes volatile organic compounds, semivolatile organics, and metals/polynuclear aromatic hydrocarbons, using default exposure factors like incidental soil ingestion rates of 100-200 mg/day for children and inhalation of resuspended particles.[78] Human health risk assessments within these frameworks adhere to a four-step paradigm: hazard identification, which catalogs contaminants and their toxicity profiles from databases like the Integrated Risk Information System (IRIS); dose-response assessment, establishing reference doses or cancer slope factors based on empirical animal and epidemiological data; exposure assessment, quantifying pathways such as direct ingestion, dermal contact, or indirect uptake via homegrown produce; and risk characterization, integrating these to estimate non-cancer hazard quotients or cancer risks, often targeting an excess lifetime cancer risk of 10^{-6} to 10^{-4}.[79] For soil-specific evaluations, bioavailability adjustments account for factors like soil pH and organic matter content, which influence metal solubility and absorption, reducing overestimation in conservative defaults. Uncertainties arise from inter-individual variability in susceptibility, such as higher risks in children due to hand-to-mouth behavior, and are addressed through sensitivity analyses.[78] Ecological risk frameworks parallel human health models but focus on terrestrial and soil biota, using eco-soil screening levels (Eco-SSLs) for contaminants like cadmium or polycyclic aromatic hydrocarbons that affect invertebrates, plants, and wildlife. The EPA's ecological guidance derives these levels from no-observed-adverse-effect concentrations in toxicity tests, incorporating food chain modeling for higher trophic levels, such as earthworm bioaccumulation leading to bird exposure.[80] Tiered evaluations start with generic benchmarks, escalating to probabilistic methods like species sensitivity distributions if site data indicate potential impacts on biodiversity or soil functions like nutrient cycling. Internationally, the ISO 19204:2017 standard outlines a TRIAD approach for site-specific ecological assessments, combining chemical analysis, ecotoxicity bioassays, and ecological effect observations to weigh evidence lines and derive integrated risk estimates.[81] These frameworks emphasize causal linkages, such as contaminant persistence and leaching potential influencing groundwater risks, while acknowledging limitations like incomplete toxicity data for mixtures or climate effects on degradation rates. Regulatory applications, including the EPA's cumulative risk framework, extend evaluations to multiple contaminants and stressors for holistic site management.[82] Empirical validation through field monitoring ensures predictions align with observed outcomes, prioritizing remediation where risks exceed acceptable thresholds based on verifiable exposure data.Impacts
Human Health Consequences
![E-waste contamination in Agbogbloshie, Ghana][float-right] Soil contamination poses significant health risks to humans through direct exposure via ingestion of soil particles or contaminated food, inhalation of airborne dust, and dermal contact, with children being particularly vulnerable due to higher hand-to-mouth activity and lower body weight.[11] Heavy metals such as cadmium (Cd), lead (Pb), arsenic (As), and mercury (Hg) accumulate in agricultural soils from industrial activities, mining, and fertilizers, entering the human body primarily through the food chain and causing bioaccumulation.[14] [47] Cadmium exposure from contaminated soil and crops leads to renal tubular dysfunction, osteoporosis, and increased cancer risk, with epidemiological studies linking soil Cd levels to higher incidences of Itai-itai disease in historically polluted areas.[47] Lead in soil dust contributes to neurodevelopmental deficits in children, including reduced IQ and behavioral issues, as well as cardiovascular disease in adults (odds ratio 1.44, 95% CI 1.17–1.76).[11] [47] Arsenic contamination, affecting 14–17% of global cropland, is associated with skin lesions, cardiovascular mortality (hazard ratio 1.28, 95% CI 1.08–1.52), and cancers of the lung, bladder, and skin.[14] [11] Organic pollutants like polycyclic aromatic hydrocarbons (PAHs) from industrial and traffic sources in soil result in cancer risks exceeding acceptable levels (10⁻⁶) in urban and industrial areas, primarily through dermal absorption (61–79% of exposure) and ingestion, with benzopyrene and indeno[1,2,3-c,d]pyrene driving the highest carcinogenic potentials.[83] Pesticide residues persisting in soil, including organochlorines and organophosphates, are linked to elevated risks of cancers (e.g., lung, ovarian), Parkinson's disease, asthma, and reproductive disorders via oxidative stress and endocrine disruption.[47]| Contaminant | Primary Exposure Pathway | Key Health Outcomes | Evidence |
|---|---|---|---|
| Cadmium (Cd) | Ingestion via crops | Renal damage, osteoporosis, cancer | Bioaccumulation in plants; linked to musculoskeletal diseases[47] |
| Lead (Pb) | Inhalation/ingestion of dust | Neurological deficits, CVD, anemia | OR 1.44 for CVD; developmental toxicity in children[11] [47] |
| Arsenic (As) | Food chain | Skin lesions, cancer, CVD mortality | HR 1.28 for CVD death; 14–17% cropland affected globally[11] [14] |
| PAHs | Dermal/ingestion | Lung/skin cancer | CR up to 4.13E-05 in high-exposure areas[83] |
| Pesticides | Ingestion/inhalation | Cancer, neurological disorders | Oxidative stress; increased Parkinson's risk[47] |