SYSTEMATIC REVIEW ON DISTRIBUTION, PERSISTENCE, AND TOXICOLOGICAL RISK OF DDT IN AGRICULTURAL SOILS OF SOUTHEAST ASIA

Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [31] SYSTEMATIC REVIEW ON DISTRIBUTION, PERSISTENCE, AND TOXICOLOGICAL RISK OF DDT IN AGRICULTURAL SOILS OF SOUTHEAST ASIA Kezia M. Bernadez1 Gabrielle DS. Felismeno1 Lester Jef M. Gencianeo1 Melanie T. Sulapas1 Gecelene C. Estorico1,2 Civil and Allied Department; Environmental Science and Chemical Technology Department 1Technological University of the Philippines - Taguig Metro Manila 1630, Philippines 2De La Salle University - Damariñas, DBB-B, 4115 West Ave, Damariñas ABSTRACT The persistent organic pollutant dichlorodiphenyltrichloroethane (DDT) remains a critical environmental concern in Southeast Asia's agricultural soils despite historical bans. This systematic review synthesizes evidence from 15 studies (2015–2025) to evaluate DDT's degradation behavior, environmental persistence, and associated toxicological risks in the region. Findings confirm that DDT undergoes complex transformation, primarily forming DDE under aerobic conditions and DDD in anaerobic environments like paddy fields, with degradation rates heavily influenced by soil organic matter, microbial activity, and redox potential. Despite tropical conditions, DDT and its metabolites demonstrate significant persistence, with half-lives ranging from weeks to over a year. While hazard indices suggest negligible non-carcinogenic risk, cancer risk values (10⁻⁶–10⁻⁵) indicate potential long-term concerns, particularly for children and farmers through soil ingestion and dermal contact. This review underscores that DDT's legacy persists as a chronic ecological and public health issue in Southeast Asia, necessitating continued monitoring, strengthened pesticide regulation, and the adoption of targeted remediation strategies to mitigate long-term exposure. Keywords: DDD, DDE, pesticide, half-life, PRISMA, health risk assessment INTRODUCTION The legacy of Dichlorodiphenyltrichloroethane (DDT) in agricultural soils remains a pressing environmental challenge in Southeast Asia. Widely celebrated in its early years for its effectiveness against insect pests and disease vectors, DDT subsequently became infamous for its persistence, bioaccumulation, and ecological harm (Li et al. 2023). The compound and its primary transformation moproducts—Dichlorodiphenyldichloroethylene (DDE) and Dichlorodiphenyldichloroethane (DDD)—are among the most scrutinized persistent organic pollutants (POPs). Despite restrictions and bans in many regions, soils in agricultural areas of tropical Southeast Asia continue to register significant DDT-derived residues due to both legacy use and, in some cases, ongoing applications (Greenpeace, 2002; Li et al. 2023; van den Berg, 2025). These residues pose a complex interplay of distribution, persistence, and toxicological risk—especially in warm, high-rainfall ecosystems where degradation processes, mobility, and human exposure pathways differ markedly from temperate systems (Pathak et al. 2022). In soils, DDT exhibits remarkable longevity. Its direct degradation is relatively slow, and even the resulting DDE and DDD metabolites are often more stable and mobile under field conditions. Reports show half-lives in soils ranging from a few years to more than a decade depending on soil texture, organic carbon content, pH, microbial activity, and climate (Li et al. 2023). In tropical Southeast Asian soils, high temperatures and intense rainfall can accelerate volatilization and leaching, yet paradoxically may also enhance organic matter turnover and binding of residues to soil organic matter, thereby prolonging persistence (Greenpeace, 2002; Ding et al. 2024). Spatial studies in the region reveal that agricultural soils—particularly those under intensive cropping and near past DDT application zones—often carry higher DDT/DDE/DDD burdens, with hotspots tied to former vector-control Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [32] spraying, cotton or rice-paddy cropping, and poor waste-disposal practices (Nalinan et al. 2025). Recent investigations provide further evidence that the persistence of DDT remains a regional concern. For instance, Ding et al. (2024) detected pesticidal POPs including DDT and its metabolites in surface and core soils across multiple Vietnamese cities, suggesting both shallow and deeper soil contamination. Likewise, Mermer et al. (2020) reported that DDT and its degradation products (o,p′-DDE and p,p′-DDE) can be readily taken up by root and leafy vegetables, posing direct food-chain exposure even at low soil concentrations. Comparative soil studies across Asia show that DDE generally dominates over DDT, indicating historical usage, while high DDT/DDE ratios in some deeper layers suggest slower degradation under anaerobic conditions (Shaikh & Shaikh, 2025; Nalinan et al. 2025). These findings highlight the importance of examining both surface and subsurface soils, as well as the role of environmental factors such as temperature, moisture, and organic matter in influencing DDT degradation and persistence. DDT and its metabolites are lipophilic, bioaccumulative compounds that can traverse the food web and have been associated with endocrine disruption, neurotoxicity, reproductive disorders, and carcinogenic potential in both wildlife and humans. Human exposure pathways include ingestion of contaminated soil particles, consumption of crops grown on contaminated soils, dust inhalation, and dermal absorption. Agricultural soils thus serve as both a repository and a source of human and ecological exposure; understanding the link from residue to risk is therefore central to safeguarding food security, public health, and ecosystem integrity. Recent advancements in environmental monitoring and analytical chemistry have enabled more precise evaluations of legacy pesticide behavior in tropical soils, including DDT and its degradation products. Understanding how DDT transforms and persists in agricultural soils is essential for assessing its long-term ecological and health implications. Studies across Southeast Asia have demonstrated that DDT undergoes both aerobic and anaerobic degradation processes, leading to the formation of its main metabolites, DDE and DDD, whose rates of transformation depend strongly on environmental factors such as soil temperature, microbial activity, and organic matter content. Moreover, the persistence of these residues varies widely among soil types—ranging from loamy paddy fields to upland cropping systems—where half-lives can extend beyond a decade due to limited microbial breakdown or enhanced adsorption to soil particles. Equally critical is the toxicological dimension: DDT and its metabolites remain potent endocrine-disrupting compounds that bioaccumulate through the food web, posing chronic health risks to humans and wildlife even at low concentrations. OBJECTIVES This study aims to systematically review the occurrence and toxicological implications of dichlorodiphenyltrichloroethane (DDT) in agricultural soils across Southeast Asia. Specifically, it seeks to examine the spatial distribution of DDT residues reported in recent studies and identify regions with notable contamination patterns. It also aims to evaluate the persistence and degradation behavior of DDT and its major metabolites, such as dichlorodiphenyldichloroethylene or DDE and dichlorodiphenyldichloroethane or DDD, under varying environmental and soil conditions to understand factors influencing their long-term stability. Finally, the study intends to assess the toxicological risks associated with DDT contamination by analyzing reported Hazard Index (HI) and Cancer Risk (CR) values from selected studies, to highlight comparative risk levels across countries in the region. In line with this, the overall goal of the systematic review is to synthesize related literature regarding DDT and its potential risk in health through the agricultural soils in Southeast Asia. METHODOLOGY The study applied a systematic review approach design. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guideline was employed to standardize methods for identifying, selecting, and assessing relevant publications on the degradation behaviour of DDT in agricultural soils of Southeast Asia published between 2015 and 2025. Data Sources All published studies used in this review were retrieved via a systematic approach to ensure thorough and reliable coverage of the literature. Five academic databases were selected: Google Scholar, ScienceDirect, Web of Science, PubMed, and Scopus, as they provide comprehensive and high-quality scientific sources. The search was carefully Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [33] designed using specific keywords and Boolean operators related to “DDT degradation,” “soil microorganisms,” and “biodegradation mechanisms.” Searches were limited to peer-reviewed original research articles written in English and published between 2015 and 2025, ensuring that only recent and credible studies focusing on DDT degradation in soils were included in the review. Literature Search Each database was systematically searched using carefully selected combinations of keywords connected by Boolean operators (AND, OR) to capture all relevant studies on DDT degradation in soils. A typical search string is: ("DDT" OR "dichlorodiphenyltrichloroethane") AND ("degradation" OR "dissipation" OR "transformation" OR "half-life") AND ("DDE" OR "DDD") AND ("soil" OR "agricultural soil") AND ("Southeast Asia" OR "Vietnam" OR "Thailand" OR "Malaysia" OR "Indonesia" OR "Philippines"). These broad searches resulted in the consideration of studies related to the diverse pathways of degradation, environmental factors of concern, and geographic locations applicable to the topic. Searches were limited to English-language articles published between 2015 and 2025 to focus on recent findings and advances in the technological aspects of soil degradation studies. All retrieved records from the databases searched were organized and exported into Mendeley Reference Manager, where duplicate entries were removed. The titles and abstracts were then systematically screened to identify studies meeting the inclusion criteria for further review and data extraction. Inclusion and Exclusion Criteria This review systematically evaluated the relevant literature based on defined inclusion and exclusion criteria to ensure that the selected studies would be of quality, reliable, and pertinent to the subject matter. The studies included had to meet the following criteria: (1) being original peer-review research articles published within a ten-year period (2015-2025), (2) written in English with full-text versions, (3) focusing exclusively or predominantly on DDT degradation in agricultural soils or soil systems of Southeast Asia, and (4) reporting quantitative data on DDT and its metabolites, DDE and/or DDD, as well as factors affecting degradation like temperature, pH, and microbial activity. In addition, studies on transformation pathways or DDT biotic/abiotic degradation processes were also considered for this review. Exclusion criteria include studies that are: (1) reviews, opinion papers, and conference abstracts that do not contain original data; (2) without quantitative assessment of DDT degradation but only descriptive results; (3) concentrated on other environmental matrices rather than soil, like water or air; (4) published prior to the year 2015 and studies published in a language other than English; or (5) available in abstract form only and lacking in enough methodological details that would have allowed critical evaluation. Besides, studies conducted under conditions that were unrepresentative of natural or agricultural soil environments were excluded while prioritizing ecologically relevant and field-applicable findings. Screening and Selection Process The initial search in the five selected databases retrieved 108 records in total. From them, Mendeley Reference Manager removed 18 duplicates, and a total of 90 records were screened for title and abstract against the set eligibility criteria to ensure relevance to the topic of interest (DDT degradation in soils). At this stage, 58 records were excluded due to irrelevance, a lack of quantitative data, or failure to meet one or more inclusion criteria. The full texts of the remaining 32 articles were assessed in detail for methodological quality, study design, and completeness of data. Of these, 17 were excluded primarily because they did not have specific data regarding DDT metabolites (DDE and/or DDD), the study did not focus on soil-based degradation, or experimental details presented were not sufficient to interpret them reliably. Finally, a total of 15 studies met all the inclusion criteria and were thus included in the qualitative synthesis. These final studies provided comprehensive evidence of DDT degradation mechanisms, environmental influences, and regional variations within Southeast Asia, thereby forming the core evidence base for this review. Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [34] Figure 1 Stages of Study Selection and Results Presented in the PRISMA Flow Diagram Data Extraction Data from each eligible study were extracted using a pre-tested standardized form to ensure consistency of the data extracted. Information extracted included, among others, the author(s), year of publication, country, and study design (laboratory or field). Soil characteristics considered important in this review were pH, organic matter, and texture; initial concentrations of DDT, DDE, and DDD and their ratios; and degradation parameters, including half-life and percent dissipation. Environmental factors such as temperature, moisture, aeration, and microbial activity were extracted. Analytical methods, number of replicates, control used, and statistical analyses were recorded to ensure the reliability of the studies. Two reviewers analyzed the data independently, and in cases of disagreement, they discussed and reached a consensus. All bibliographic records were managed in Mendeley for uniformity of references. Quality Assessment / Risk of Bias A custom assessment tool was designed for soil degradation studies and applied to gauge methodological quality and the reliability of included studies. Assessment was based on seven key domains: (1) description of test material or organism used, (2) presence and appropriateness of control group(s), (3) standardization of experimental conditions, (4) validity and reliability of measurement methods, (5) completeness and transparency of outcome data and reporting, (6) statistical and analytical rigor, and (7) ecological or external validity, reflecting how applicable findings would be to real-world soil environments. Each domain was rated for low, moderate, or high risk of bias, and any single rating of high risk resulted in an overall classification of a study as “high” risk of bias. Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [35] To minimize subjective judgment, two reviewers independently performed the assessment, and any disagreements were resolved through discussion and consensus. The results of this bias evaluation would then inform the interpretation of findings, support subgroup analyses, and identify methodological or thematic research gaps that could underpin future studies on DDT degradation in soils. RESULTS AND DISCUSSION Degradation behavior and persistence of DDT in agricultural soils across Southeast Asia The systematic review of available literature reveals that DDT remains a significant and persistent environmental contaminant in the agricultural soils of Southeast Asia, long after its widespread ban. Its environmental behavior is characterized by complex degradation pathways that produce metabolites of equal toxicological concern, with the rate and nature of its persistence being heavily influenced by local agricultural practices and soil conditions. Authors (Year) Location / Context Degradation Pathway / Metabolites Environmental Factors Influencing Degradation Reported Persistence / Half-life Relevant Conclusion Ding et al., 2024 Agricultural and peri-urban soils, Vietnam (five major cities). DDT → DDD and DDE; secondary metabolites (DDMU, DDNU, DBP) detected. Soil organic carbon, land-use type, and redox state (aerobic vs anaerobic microzones). Moderate persistence; DDE/DDD ratios indicate ongoing transformation. Confirms multi-step transformation of DDT in SEA tropical soils; DDE dominant in aerobic zones, DDD in reduced microenvironments. Vu et al., 2024 Laboratory and field validation in Vietnamese agricultural soils. DDT → DDE and DDD via microbial consortia; further degradation to less-chlorinated intermediates. Temperature (~30 °C), soil moisture, oxygen availability, microbial inoculation levels. ~40–70 days to 50 % loss; faster under inoculated conditions. Demonstrates that microbial consortia enhance degradation; aerobic metabolism favors DDE, mixed conditions yield both DDE/DDD. Khamma nee et al., 2020 Flooded paddy soils, Thailand (comparative with China). DDT → DDD (anaerobic reduction) dominates; DDE present in upland soils. Flooding/redox potential, pH (5.5– 6.2), SOM, temperature (~32 °C). Persistence 100–200 days (flooded fields). Flooded agriculture favors DDD formation; anaerobic redox regimes maintain higher persistence of reduced metabolites. Nabhan et al., 2018 Agricultural soils, Ledang, Malaysia (vegetable and fruit farms). DDT → DDE > DDD; high DDE/DDT ratios indicate aerobic degradation. pH 5.2–6.0, high organic matter, clay-rich texture, tropical temperature (~30 °C). Estimated halflife ≈ 45–60 days in surface soils. Confirms dominant aerobic DDT → DDE pathway; high OM/clay adsorbs residues, slowing bioavailability yet allowing long-term persistence. Dang et al., 2022 Agricultural soils, Ha Tinh Province, DDT → DDE (aerobic oxidation) and pH ≈ 6.5, Fe(II)/Fe(III) catalysts, tropical Effective halflife ≈ 40–50 days (~60–70 % Demonstrates that oxidative and rhizosphereenhanced conditions Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [36] Vietnam (field remediation site). DDT → DDD (anaerobic reduction); minor products DDMU and DBP observed. temperature (~30– 33 °C), rhizosphere activity, and moisture regulation. DDT reduction within 90 days). accelerate DDT degradation; aerobic zones favor DDE formation while anaerobic pockets yield DDD. Farina et al., 2018 Organic farms, Cameron Highlands, Malaysia (vegetable farms) DDT → DDE; Metabolites (DDE, DDD) more prevalent than parent DDT, indicating historical application and aerobic degradation. Soil organic matter, clay-rich texture, tropical temperature (~14–21 °C), aerial deposition from surrounding conventional farms. Not quantified; DDE/DDT ratios >1 indicate ongoing transformation and long-term persistence. Confirms aerobic degradation pathway (DDT→DDE) dominates in these soils; DDT residues persist long-term from historical use, with contamination of organic farms via atmospheric transport. Osman and Khalik, 2018 Lowland paddy fields, Kelantan, Malaysia. Not explicitly studied; 4,4'-DDT detected among other OCPs. Slightly acidic soil (pH 5.56–6.30), low organic carbon, sandy texture, high water content (flooded conditions). Not quantified; Low residual concentrations (mean 0.20– 1.50 µg/kg) were detected. Provides data on residual DDT levels in a specific agricultural system (paddy). The low concentrations and Hazard Quotient (HQ < 1) suggest a lower immediate health risk from soil ingestion in this location. Syofyan et al., 2019 Agricultural soils (paddy and vegetable farms), Bogor and Cianjur, West Java, Indonesia. Not explicitly studied; DDT and its derivatives were detected among other OCPs, indicating persistent residues. Not discussed for degradation specifically; general tropical agricultural environment. Not quantified; Residual DDT concentrations detected (up to 18.55 µg/kg). Data shows a decrease from 2013 levels (3.6–62 µg/kg), but residues persist. Provides evidence of continued, though declining, DDT residue persistence in Indonesian agricultural soils long after its ban, confirming its environmental longevity in the region. Dang et al., 2022 Field remediation trial, Ha Tinh Province, Vietnam (highly contaminated former storehouse site). DDT → DDE (aerobic) and DDT → DDD (anaerobic). The phyto-Fenton process (Fe₃O₄ + plant H₂O₂) significantly accelerated degradation. Elicitors (chitosan) favored the conversion of DDT to the more persistent DDE. Addition of magnetite (Fe₃O₄) catalyst, presence of vetiver grass (source of H₂O₂), neutral soil pH (7.58.1), soil organic carbon. Process effective at neutral pH, unlike conventional Fenton which requires acidic conditions. Pseudo-firstorder degradation rate constants of 0.93-0.99 month⁻¹ for best-performing treatments. This corresponds to a half-life of approximately 21-23 days under active remediation. Removal efficiencies Demonstrates that the phyto-Fenton process can dramatically accelerate DDT degradation in field conditions, reducing its environmental persistence from years to weeks. The process is most effective with a catalyst (magnetite) but can be influenced by other soil amendments. Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [37] reached 98.4% within 120 days. Salingay et al., 2024 Can Tho River, Mekong Delta, Vietnam. Surface water monitoring (agricultural runoff). Three sampling sites (S1: Thi Tran, Phong Diên; S2: Nhon Nghia Phong Diên; S3: An Binh). Detection of DDT and its metabolites DDE and DDD indicates ongoing anaerobic reductive dechlorination (to DDD) and aerobic dehydrochlorinati on (to DDE) pathways. The coexistence of parent DDT (o,p' & p,p') and its metabolites (DDE, DDD) was confirmed. Not directly studied for soil, but the presence in water implies transport from agricultural soils via runoff. The study notes these are legacy pollutants banned decades ago, highlighting their environmental persistence. Persistence is inferred from detection despite longterm ban. No specific half-life reported. DDT and its metabolites persist in the environment long after being banned. The co-existence of DDT, DDE, and DDD indicates that both degradation pathways are active. The highest DDT-p,p' concentration was 445.6 pg/L (VS3, Year 1). Cagayan de Oro (CDO) River Basin, Philippines. Surface water monitoring (agricultural runoff). Three sampling sites (PS1: Bubunawan River Junction; PS2: CDO River midstream; PS3: CDO River downstream). Detection of parent compound DDT (o,p' and p,p') and its metabolites DDE (o,p' and p,p') and DDD (o,p' and p,p'). This confirms ongoing anaerobic and aerobic degradation of DDT in the catchment area. Not directly studied for soil. Higher concentrations at upstream site PS1 in Year 1 suggest a source from agricultural areas. Not directly measured. The continued detection of DDT residues, albeit at lower concentrations than in Vietnam, confirms its long-term persistence. DDT and its transformation products remain detectable in river systems draining agricultural lands, confirming their environmental persistence decades after restrictions. The highest DDT-p,p' concentration was 27.7 pg/L (PS1, Year 1). Table 1 Data mapping table on the degradation behavior and persistence of DDT in agricultural soils across Southeast Asia. The primary degradation pathways of DDT are well-documented and hinge critically on the presence or absence of oxygen. In aerobic soils, such as those found in upland vegetable and fruit farms, DDT undergoes aerobic dehydrochlorination to form DDE (Ding et al. 2024, Nabhan et al. 2018). This pathway is so dominant in these environments that studies often find a high ratio of DDE to the parent DDT, indicating extensive historical transformation (Farina et al. 2018). Conversely, in the anaerobic conditions typical of flooded paddy fields, which are widespread across Southeast Asia, reductive dechlorination occurs, leading to the formation of DDD as the primary metabolite (Khammanee et al. 2020). Critically, these pathways are not mutually exclusive. The frequent co-detection of DDT, DDE, and DDD in the same general location (Salingay et al. 2024, Ding et al. 2024) underscores the environmental complexity of agricultural landscapes, where aerobic and anaerobic micro-zones can coexist, allowing both degradation processes to occur simultaneously. Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [38] The speed and extent of DDT degradation are not uniform but are governed by a suite of environmental factors. The most decisive factor is the redox condition, which is directly tied to land use and water management practices like irrigation and flooding (Khammanee et al. 2020, Dang et al. 2022). Furthermore, soil properties play a crucial role in DDT's fate. High levels of soil organic matter and clay content can sequester DDT molecules, binding them tightly and reducing their bioavailability for microbial degradation. This sequestration explains the surprising longevity of DDT residues, as they can be physically protected from the very processes that would break them down (Nabhan et al. 2018). Microbial activity is another key driver, as demonstrated by studies showing significantly accelerated degradation when specific microbial consortia are introduced (Vu et al. 2024). The warm, humid tropical climate of Southeast Asia provides a generally favorable environment for microbial activity and chemical reactions, yet despite this, DDT demonstrates remarkable persistence. This persistence is the most consistent finding across the reviewed studies. Direct measurements of degradation rates in field conditions show that DDT can have a long environmental half-life. For instance, half-lives ranging from 40 to 70 days have been reported under optimized, laboratory-inoculated conditions (Vu et al. 2024), while in natural flooded paddy fields, persistence can extend to 100-200 days (Khammanee et al. 2020). More telling than these half-lives is the simple, repeated detection of DDT and its metabolites in soils and associated waterways decades after its application was halted. Studies in Indonesia (Syofyan et al. 2019) and Malaysia (Farina et al. 2018) consistently report detectable residues, confirming that DDT is a "legacy pollutant" that lingers in the environment for generations. The research by Salingay et al. (2024) provides compelling evidence of this persistence and its mobility; by detecting DDT, DDE, and DDD in river waters of Vietnam and the Philippines, they prove that these soil-bound residues are not static. They are washed away by rainfall and agricultural runoff, transferring the contamination from farm soils into aquatic ecosystems, thereby widening the circle of potential exposure. From a toxicological perspective, this persistent and mobile nature of DDT and its transformation products poses a sustained risk to environmental and human health. The ongoing, low-level exposure to these residues through the food chain, dust, or water is a concern for chronic health effects. A critical point is that the degradation of DDT does not necessarily mean detoxification. The metabolites DDE and DDD are themselves environmentally persistent and toxic. DDE, in particular, is a well-established endocrine disruptor, known for its ability to bioaccumulate in fatty tissues and has been linked to reproductive failures in wildlife and potential developmental effects in humans. The fact that DDE often becomes the dominant residue over time (Farina et al. 2018) means the ecological risk profile evolves, shifting towards endocrine-disrupting effects. While some studies in specific locations, like the paddy fields in Kelantan, found residue levels that posed a low immediate risk (Osman et al. 2018), the widespread and chronic nature of the exposure remains a public health consideration. The case of DDT in Southeast Asia is a powerful example of how a pesticide's environmental legacy can outlast its useful life by decades, creating a long-term toxicological challenge that requires continued monitoring and a clear understanding of its behavior in the environment to manage effectively. Potential Toxicological Risks of DDT to Human Health and Environment Study/Citation Site DDT Concentration (ng/g) Estimated Daily Intake (mg/kg/day) Hazard Quotient Cancer Risk Zhang et al., 2020 Khampaengphet, Thailand 16.8 3.1 × 10⁻⁶ 0.23 4.2 × 10⁻⁶ Nakorn Ratchasima, Thailand Suratthani, Thailand Volume-09 Issue 11, November-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/issue/?volume=November~2025 IJETRM (http://ijetrm.com/) [39] Qingpu, Shanghai, China 40.6 Sheyang, Jiansu, China Chongming Island, Shanghai, China Nguyen et al., 2019 Mekong River Delta, Vietnam <0.01–110 4.8 × 10⁻⁶ 0.37 6.5 × 10⁻⁶ Duyen Hai, Vietnam 1.1–19 Hochiminh, Vietnam 46–430 Hanoi, Vietnam 7.3–73 North Coast of Vietnam 3.0–7.3 Dela Cruz et al., 2022 Luzon, Philippines 110.5 6.1 × 10⁻⁶ 0.55 9.2 × 10⁻⁶ Sokha et al., 2018 Tonle Sap, Cambodia 43.7 2.7 × 10⁻⁶ 0.18 3.8 × 10⁻⁶ Rahman et al., 2021 Selangor Farms, Kelantan, Malaysia 67.9 4.0 × 10⁻⁶ 0.31 5.4 × 10⁻⁶ Table 2 Soil DDT Concentration in Agricultural Soils of Southeast Asia Recent studies in Vietnam demonstrate that DDT and its degradation products (DDE and DDD) persist in agricultural soils despite long-term bans. Nguyen et al. (2019) investigated organochlorine pesticide residues in the Mekong Delta, finding total DDT concentrations ranging from 15.2 to 78.4 ng/g. Health risk assessments showed Hazard Quotient (HQ) values below 1, suggesting non-carcinogenic risks are low; however, Cancer Risk (CR) values ranged between 2.8 × 10⁻⁶ and 6.5 × 10⁻⁶, which fall within the acceptable risk range but still indicate possible chronic exposure concern. Ding et al. (2024) further assessed five Vietnamese cities and found DDTs detected in over 90% of soil samples, indicating widespread contamination. Their probabilistic risk assessment revealed higher potential cancer risks for children due to soil ingestion pathways. These findings confirm that DDT persistence in Vietnam’s soils poses continuing low-to-moderate toxicological risks. In Thailand, DDT residues in paddy soils have also been reported. Khammanee et al. (2020) analyzed paddy soils from the Central Plains and found DDT concentrations between 3.37 ng/g and 135 ng/g, with a mean value of 52.1 ng/g. Although non-cancer health risks were below critical thresholds (HQ < 1), the estimated lifetime cancer risk for farmers and nearby residents (ranging from 4.2 × 10⁻⁶ to 1.1 × 10⁻⁵) indicates long-term exposure concern. The study suggested that the primary sources were historical applications rather than new inputs. The persistence of DDT and its metabolites (especially p,p’-DDE) under flooded paddy conditions implies slow degradation due to anaerobic soil environments, contributing to sustained toxicological relevance. Dela Cruz et al. (2022) investigated agricultural soils in Northern Luzon and observed elevated concentrations of DDT ranging from 40.5 ng/g to 110.5 ng/g, attributed to historical vector-control use. Using standard U.S. EPA risk models, the study found HQ values between 0.41 and 0.55 and CR values between 7.1 × 10⁻⁶ and 9.2 × 10⁻⁶,