Persistent Organic Pollutants In Soil Research Articles

Snow Amplification of Persistent Organic Pollutants at Coastal Antarctica.

Many legacy and emerging persistent organic pollutants (POPs) have been reported in polar regions, and act as sentinels of global pollution. Maritime Antarctica is recipient of abundant snow precipitation. Snow scavenges air pollutants, and after snow melting, it can induce an unquantified and poorly understood amplification of concentrations of POPs. Air, snow, the fugacity in soils and snow, seawater and plankton were sampled concurrently from late spring to late summer at Livingston Island (Antarctica). Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) concentrations in snow and air were close to equilibrium. POPs in soils showed concentrations close to soil-air equilibrium or net volatilization depending on chemical volatility. Seawater-air fugacity ratios were highly correlated with the product of the snow-air partition coefficient and the Henry's law constant (KSA H'), a measure of snow amplification of fugacity. Therefore, coastal seawater mirrored the PCB congener profile and increased concentrations in snowmelt due to snowpack releasing POPs to seawater. The influence of snowpack and glacier inputs was further evidenced by the correlation between net volatilization fluxes of PCBs and seawater salinity. A meta-analysis of KSA, estimated as the ratio of POP concentrations in snow and air from previously reported simultaneous field measurements, showed that snow amplification is relevant for diverse families of POPs, independent of their volatility. We claim that the potential impact of atmospheric pollution on aquatic ecosystems has been under-predicted by only considering air-water partitioning, as snow amplification influences, and may even control, the POP occurrence in cold environments.

Persistent Organic Pollutants in Soils of Southern Baikal

The concentrations of persistent organic pollutants (polychlorinated biphenyls and organochlorine pesticides) in soils of the Southern Baikal coastal zone since 1997 till 2016 have been analyzed, and the current state of the region with respect to contamination of soils by persistent organic pollutants has been assessed.

Enhanced microbial degradation of benzo[a]pyrene by chemical oxidation

Chemical oxidation and microbial degradation are promising treatments to remediate soils contaminated with persistent organic pollutants. Moderate pre-oxidation is able to enhance the subsequent bioremediation of organic pollutants in soil. In this study, the effects of pre-oxidation on the subsequent biodegradation of benzo[a]pyrene (BaP) were evaluated. The tested oxidants included potassium permanganate (PP) and iron-activated sodium persulfate (PS) at the concentration of 1–40 mmol L−1. The results showed that 20 mmol L−1 PS and 10 mmol L−1 PP treatments had the highest degradation efficiency of BaP in soil, up to 98.7% and 84.2%, without inhibiting subsequent microbial degradation. 10–20 mmol L−1 of the two oxidants significantly promoted viability of microbial community. Especially, PS facilitated the occurrence of more PAHs-degrading microorganisms. The expression of PAH-degradation gene in PS treatment was significantly higher than that in PP treatment (P < 0.05), leading to 12.0–18.4% higher degradation efficiencies of BaP. In general, proper oxidants of moderate dosages were able to promote microbial bioremediation of persistent organic pollutants in soil.

Manure amendment reduced plant uptake and enhanced rhizodegradation of 2,2′,4, 4′-tetrabrominated diphenyl ether in soil

To test whether manure amendment in soil reduces plant uptake of persistent organic pollutants, carrot (Daucus carota L.) was used as a model plant and 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47) was selected as a model persistent organic pollutant to conduct a pot experiment with contaminated soil amended by composted pig manure. The results showed that the concentration and bioconcentration factors (BCFs) of BDE-47 in the edible part of carrot significantly decreased from 229.7 ± 28.2 to 43.4 ± 20.4 ng g−1 and from 1.86 ± 0.5 to 0.15 ± 0.03, respectively, with increasing composted pig manure dose from 0 to 4%. Organic matter (OM) derived from composted pig manure played a dominant role in reducing persistent organic pollutant bioavailability in soil. Composted pig manure amendment and carrot cultivation jointly altered the bacterial community composition in soil, especially the rhizosphere. Rhizodegradation of BDE-47 was enhanced from 8.6 to 28.5% with increasing composted pig manure dose from 0 to 4%, corresponding to increased soil microbe diversity and polybrominated diphenyl ether-degrading bacteria (Sphingomonas, etc.) abundance in the rhizosphere. This study is the first, to the best of our knowledge, to provide an effective agronomic strategy of manure amendment to reduce plant uptake and simultaneously enhance rhizodegradation of persistent organic pollutants in soil, and thus potentially reduce human health risks through dietary intake.

Effect of extracellular polymeric substance components on the sorption behavior of 2,2′,4,4′-tetrabromodiphenyl ether to soils: Kinetics and isotherms

Microbial extracellular polymeric substances (EPS) and persistent organic pollutants (POPs) commonly exist in the soil environment. Currently, there is a knowledge gap regarding the effect of EPS on the fate of POPs in soil. In the present study, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was used as a model compound to investigate the effects of bovine serum albumin (BSA) and sodium alginate (SA) - mimicking the main components of EPS - on sorption of POPs to soils, through batch experiments. Irrespective of the concentration of BSA: the addition of BSA did enhance the sorption capacity of BDE-47 to soils, due to generation of more sorption sites. For SA, it increased the sorption capacity of BDE-47 at low BDE-47 concentrations, while the presence of SA negatively affected sorption of BDE-47 at high BDE-47 concentrations. The partition effect dominates the sorption of BDE-47 to soils, but after adding either BSA or SA, the sorption of BDE-47 to soils is dominated by surface sorption. Film diffusion and intra-particle diffusion were also involved in the sorption process with and without BSA or SA, with the latter being the rate-limiting step. The heterogeneous surface and nonlinear sorption behavior of BDE-47 to soils increased in the presence of either BSA or SA. The FTIR spectra indicated that the aromatic CC, H-bonds and OH groups may be involved in the sorption process. Therefore, BSA enhanced the retention of BDE-47 to soil, while SA's influence on BDE-47 sorption to soil depended on the concentration of BDE-47.

A review of POPs in the fragile critical zone of the Tibetan Plateau: transport and transformation

The near-surface environment of the Tibetan Plateau is a fragile critical zone. Our understanding of the transport and transformation of persistent organic pollutants (POPs) in the ecosystem has significantly improved with research conducted in recent decades. In the current study, POP concentrations in soils logarithmically decreased and fractionated with increasing distance from the source area, patterns attributed to air–soil exchange. Transport from soils resulted in the enrichment of POP concentrations in plants and sediments. The enantiomeric fraction indicated that transformation of POPs in soils was significantly correlated with altitude. At the same time, the chiral signature of POPs in soils was maintained from soils to sediments, while the chiral transformation from soils to plants was found to be complex.

The effective migration of Massilia sp. WF1 by Phanerochaete chrysosporium and its phenanthrene biodegradation in soil

Pollutant-degrading bacteria migrated by fungi may enhance the contacts between microorganisms and pollutants and improve the bioremediation efficiency of persistent organic pollutants in soil. Here, the migration of phenanthrene (PHE)-degrading bacteria Massilia sp. WF1 and Mycobacterium sp. WY10 by the hydrophobic fungi Phanerochaete chrysosporium (P. chrysosporium) and its effects on the PHE biodegradation in soil were investigated. Migration of the hydrophilic bacterium WF1 was better than that of the hydrophobic bacterium WY10 by P. chrysosporium mycelia since strain WF1 possesses flagellum and the type III secretion system. The interaction energy change of P. chrysosporium-WF1 was lower, but the interaction forces (van der Waals attractions, capillary forces, and cross-linking effects) were stronger than those of P. chrysosporium-WY10. Thus, the adhesive attraction between strain WF1 and P. chrysosporium was stronger, and consequently, strain WF1 was migrated by P. chrysosporium to a greater extent than WY10. The corresponding migration mechanism was inferred to be a bacterial ‘passive’ method: bacteria adhered to mycelia before they migrated with the growing mycelia. Moreover, migrated strain WF1 via P. chrysosporium showed effective PHE biodegradation in soil. Fungus-mediated migration of pollutant-degrading bacteria may play an important role in the bioremediation of pollutants in soil.

Novel Biochar-Plant Tandem Approach for Remediating Hexachlorobenzene Contaminated Soils: Proof-of-Concept and New Insight into the Rhizosphere.

Volatilization of semi/volatile persistent organic pollutants (POPs) from soils is a major source of global POPs emission. This proof-of-concept study investigated a novel biochar-plant tandem approach to effectively immobilize and then degrade POPs in soils using hexachlorobenzene (HCB) as a model POP and ryegrass (Lolium perenne L.) as a model plant growing in soils amended with wheat straw biochar. HCB dissipation was significantly enhanced in the rhizosphere and near rhizosphere soils, with the greatest dissipation in the 2 mm near rhizosphere. This enhanced HCB dissipation likely resulted from (i) increased bioavailability of immobilized HCB and (ii) enhanced microbial activities, both of which were induced by ryegrass root exudates. As a major component of ryegrass root exudates, oxalic acid suppressed HCB sorption to biochar and stimulated HCB desorption from biochar and biochar-amended soils, thus increasing the bioavailability of HCB. High-throughput sequencing results revealed that the 2 mm near rhizosphere soil showed the lowest bacterial diversity due to the increased abundance of some genera (e.g., Azohydromonas, Pseudomonas, Fluviicola, and Sporocytophaga). These bacteria were likely responsible for the enhanced degradation of HCB as their abundance was exponentially correlated with HCB dissipation. The results from this study suggest that the biochar-plant tandem approach could be an effective strategy for remediating soils contaminated with semi/volatile organic contaminants.

Source identification and health risk assessment of Persistent Organic Pollutants (POPs) in the topsoils of typical petrochemical industrial area in Beijing, China

Thirty-one topsoil samples were collected from the area of the Yanshan petrochemical industries to comprehensively determine the spatial distribution, the possible sources and the potential risks of legacy Persistent Organic Pollutants (POPs) in a typical petrochemical industrial area. The total concentration of 16 PAHs, predominantly originated from the local emission from fuel combustion, ranged from 35.29 to 6120.22ng/g with a mean value of 906.11ng/g. Organochlorine Pesticides (OCPs) originated mainly from the recent inputs and their total concentrations varied from 4.13 to 7215.24ng/g with a mean of 336.13ng/g. Polychlorinated Biphenyls (PCBs) were associated with the usage of commercial products and the total concentrations of 125 congeners ranged from 2.21 to 4008.47ng/g with a mean of 486.12ng/g. Residential Total Lifetime Carcinogenic Risk (TLCR) value, higher than the target excess individual lifetime risk (1×10−6), was calculated to be of 22.6% for PAHs, 16.1% for OCPs and 6. 5% for PCBs respectively. Occupational TLCR, higher than the target excess individual lifetime risk was of 9.7% for PAHs, 6.5% for OCPs and 0% for PCBs respectively. In all sampling sites, non-carcinogenic risks expressed as Total Hazard Quotient (THQ) for PAHs, OCPs and PCBs were always below 1. As a consequence, the carcinogenic and non-carcinogenic risks due to exposure to POPs in soil were very low even in such a typical petrochemical industrial area. In the study, the management and the risk assessment of POPs in a petrochemical industrial area close to a metropolis, were evaluated comprehensively.

Content of radionuclides and persistent organic pollutants in agricultural soils after the Chernobyl nuclear power plant accident

The results of dosimetry measurements and determination of radionuclides, pesticides, and persistent organic pollutants in agricultural soils 24 years after the Chernobyl nuclear power plant accident are reported. A comprehensive analysis of soils from nine different sites in the Oryol oblast was carried out in May, 2010. The exposure dose rate at 1 m above the ground varied from 12.3 to 20.1 mR/h, indicating a significant decrease since 1986. The annual radiation dose to the population of the villages surveyed was above the statutory level (1.3–1.8 mSv/year versus 1 mSv/year). The contents of 137Cs and 40K in soils at the examined sites ranged, respectively, from 0.09 to 0.63 and from 0.48 to 0.71 kBq/kg dry mass weight. The downward vertical migration of radionuclides deep into the soil was detected. Concurrent qualitative and quantitative measurements of pesticides and persistent organic pollutants in soil samples were performed. Pesticides were detected at all sites. Although the soil in some areas was found to contain small amounts of pollutants, the overall environmental situation can be qualified as unfavorable. It was concluded that the use of pesticides should be limited, measures should be undertaken to remove residual amounts of radionuclides, pesticides, and POPs, and conditions for environmentally friendly agricultural production should be provided.

Fate of POPs and its Laboratorial Technics under Combined Plants Cultivation

The removal of persistent organic pollutants (POPs) in soils at initial concentrations ranging from 20.00 to 321.05 mg·kg-1 was investigated under different planting patterns, and enhancement mechanisms were analyzed. Results showed that the dissipation of POPs in soils growing Brassica campestris and Medicago sativa significantly exceeded those vegetating single species. During 70-day experiment, about 75.06% of Pyr and 68.22% of BaP was removed from the soils under mixed cropping; while only 31.8% and 64.03% of Pyr and 27.84% and 51.93 of BaP were removed under single rape and alfalfa cropping, respectively. Of all pathways enforcing POPs removal, plant-microbial interactions is the most predominant. These results suggested a feasibility of the establishment of multi-species phytoremediation for improvement of the remediation efficiencies of POPs, which may decrease accumulations of POPs in crops and thus reduce their risks.

Enhanced Dissipation of POPs in Soils by Combined Plants Cultivation

The removal of persistent organic pollutants (POPs) in soils at initial concentrations ranging from 20.00 to 321.05 mg·kg-1 was investigated under different planting patterns, and enhancement mechanisms were analyzed. Results showed that the dissipation of POPs in soils growing Brassica campestris and Medicago sativa significantly exceeded those vegetating single species. During 70-day experiment, about 75.06% of Pyr and 68.22% of BaP was removed from the soils under mixed cropping; while only 31.8% and 64.03% of Pyr and 27.84% and 51.93 of BaP were removed under single rape and alfalfa cropping, respectively. Of all pathways enforcing POPs removal, plant-microbial interactions is the most predominant. These results suggested a feasibility of the establishment of multi-species phytoremediation for improvement of the remediation efficiencies of POPs, which may decrease accumulations of POPs in crops and thus reduce their risks.

Assessment of limit values of risk elements and persistent organic pollutants in soil for Czech legislation

The proposal of hierarchical limit system of risk elements (RE) and persistent organic pollutants (POPs) for agricultural soils is presented. The system is not proposed for forest soils (limits are still missing in the Czech Republic). Two levels of limit values were proposed. The first one is the prevention limit statistically derived from the background values of RE and POPs in Czech agricultural soils. The second one is indication limit derived from the risk of plant growth inhibition (RE phytotoxicity effects where the results of experimental trials were utilised), the risk of food chain contamination (RE transfer from the soil into the plants where the results of experimental trials testing the transfer of RE from soils into plants were used) and human health risks (RE and POPs inhalation, dermal and oral intake where the model following US EPA methodology was calculated). The limit values system should replace current version of legislative norm &amp;ndash; Decree No. 13/1994 Coll. The principles of limit values assessment for individual levels of the limits are described.

Distributions of new Stockholm Convention POPs in soils across South Korea

In this study, we monitored the newly added Stockholm Convention persistent organic pollutants (POPs) HCHs, PeCBz, endosulfans, chlordecone, PBDEs, PBBs and PFCs in industrial, urban, and agricultural soils in South Korea, in order to evaluate their distributions and potential sources. These POPs were widely distributed throughout South Korea, and their concentrations and distributions were affected by land use, reflecting their sources. The overall concentrations of HCHs, PeCBz, endosulfans, PBDEs, and PFCs in soils were in the range of ND (non-detectable)–0.358ng/g (average±standard deviation: 0.060±0.080ng/g), ND–0.531ng/g (0.083±0.133ng/g), 0.058–8.42ng/g (2.19±2.43ng/g), 0.004–4.78ng/g (0.68±1.06ng/g), and ND–1.62ng/g (0.50±0.46ng/g), respectively. Agricultural soils showed the highest concentration of endosulfan, which was the most recently used pesticide monitored in this study. On the other hand, industrial soils contained the highest concentrations of PeCBz, PBDEs, and PFCs, which were mainly introduced to environment via the industrial activities.

Persistent organic pollutants in soil near the Changwengluozha glacier of the Central Tibetan Plateau, China: Their sorption to clays and implication

Twenty-seven soil samples were collected at ca. 5000m from the Changwengluozha glacier. In addition to soil components, the concentration of 23 organochlorine pesticides (OCPs) and 16 polycyclic aromatic hydrocarbons (PAHs) were analyzed. Clay minerals were found to play a key role in the accumulation of OCPs/PAHs in soil. The sorption ratio of chemical to clay was ordered in the OCPs and PAHs to the vapor pressure in a negatively correlated fashion. Because of the negative relationship between vapor pressure and the soil–air partition coefficients (KSA), it was understood that the higher sorption ratio responded to a higher KSA, which indicated the fate of the contaminants in soil. The soil near the Changwengluozha glacier functioned as a “sink” for OCPs in the decreasing order of 2,4′-DDT, 4,4′-DDD, HCB, δ-HCH, and α-HCH and for PAHs in an decreasing order of Pyr, Flu, Fl, Ace, and Acy.

Altitudinal and Spatial Signature of Persistent Organic Pollutants in Soil, Lichen, Conifer Needles, and Bark of the Southeast Tibetan Plateau: Implications for Sources and Environmental Cycling

The southeast Tibetan Plateau (TP) of China is characterized by mountain-valley topography and is usually the main channel for the warm and humid airstream from South Asia caused by the Indian monsoon. In this study, it is hypothesized that some semivolatile organic pollutants such as organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) can be transported from the densely populated and intensely agricultural Indian Subcontinent via the Indian monsoon and then cold-trapped by the mountains of the southeast TP. Samples of soils, lichens, conifer barks, and needles were collected from five transects to investigate the accumulation patterns of OCPs and PAHs in this region. The OCP concentrations were found to generally increase with increasing altitude in transects 1, 3, and 4, while such trends were insignificant in most cases for PAHs. Total organic carbon/lipid based normalization of concentrations does not strengthen the correlations with altitude in most cases. Chemical concentration ratios in soils of forest areas to clearing sites without forest cover (F/C) showed significantly positive correlation with log K(oa) and negative correlation with log K(aw) of PAHs, suggesting that the role of forests as a filter and forest soil as a final sink are more pronounced for more lipophilic compounds. A lower α-/γ-HCH ratio and higher ratios of DDT/DDE and o,p'-DDT/p,p'-DDT compared with the technical products suggest the usage of lindane (γ-HCH), DDT, and dicofol in neighboring countries. The suitability of using different sample matrices (soil, lichen, conifer bark, and needles) as passive air samplers in remote regions is evaluated.

Fate and plant uptake of persistent organic pollutants in soil

Many persistent organic pollutants (POPs), notably hexachlorocyclohexanes (HCHs), chlorinated cyclodienes, and dichlorodiphenyltrichloroethanes (DDTs), remain in Japanese farming soils, more than 40 years after their use as insecticides was prohibited. In recent years, residues of chlorinated cyclodienes in cucurbit fruits have become a problem. But, though HCHs and DDTs have been staying in the soil, residues of these chemicals in crops have not been a problem. So we compared the fates of HCHs (α-, β-, γ-HCHs), chlorinated cyclodienes (dieldrin, endrin, heptachlor exo-epoxide), and DDTs (DDE, dichlorodiphenyldichloroethylene; DDD, dichlorodiphenyldichloroethane) in soil and investigated their uptake by several non-cucurbits and cucurbits. As for the fate of POPs in soil, not only the total concentrations but also the concentrations in soil solution as bioavailable POPs were determined. The half-lives of total β-HCH and DDTs in soil were the longest, and α- and γ-HCHs the shortest. On the other hand, the half-lives of bioavailable POPs ranged from 1/3 to 1/20 of those of total POPs. The ratio of the half-lives of bioavailable POPs to those of total POPs decreased in the order of HCHs > chlorinated cyclodienes > DDTs. Because hydrophobic chemicals were adsorbed strongly to the soil, the bioavailable POPs in soil are controlled by their hydrophobicity, indicated by the values of log K OW (K OW: n-octanol-water partition coefficient). The shoot concentrations of chlorinated cyclodienes and DDTs were higher in cucurbits than in non-cucurbits. However, among POP insecticides, HCHs did not show clear differences. As for the root concentrations, all tested POPs were higher in cucurbits than in non-cucurbits. Through the determination of POPs in soil solution, we could compare the abilities of plants to take up the chemicals using soil solution bioconcentration factors (BCFSS). The values of BCFSS increased with the magnitude of log K OW, in the order of HCHs < chlorinated cyclodienes < DDTs. In addition, BCFSS did not show marked differences among isomers or chemicals with similar structure. Therefore, plant uptake ability was influenced mainly by log K OW. After being applied to agricultural land, α- and γ-HCHs seemed to disappear quickly, β-HCH persisted longer but the uptake in roots was low because of the low log K OW, and DDTs also persisted longer but the bioavailability decreased rapidly in the soil because of their high log K OW. Chlorinated cyclodienes have remained in the soil and have remained available, because they are less likely than HCHs (except β-HCH) to disappear and less likely than DDTs to become adsorbed to the soil. In addition, their higher log K OW than that of HCHs makes them more easily taken up by roots. However, shoot concentrations were high only in cucurbits, for which they remain a problem in Japan.

Temporal trends of PCBs, PCDD/Fs and PBDEs in soils from an E-waste dismantling area in East China

The temporal trends of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polybrominated diphenyl ethers (PBDEs) were investigated in soils from an E-waste dismantling area in East China between 2005 and 2011. Isotope dilution high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) was employed for the sample analysis. PCB levels declined as expected, while PCDD/Fs generally remained at a constant level during the sampling period, and PBDE concentrations tended to be slightly lower after 2007 although the decline was not statistically significant. The congener profiles indicated that lowly-halogenated congeners of these persistent organic pollutants (POPs) accounted for the decreasing levels and relative proportions of the POPs, suggesting that they have been gradually eliminated from the field soil over the years. However, the concentration levels of some heavy congeners (e.g., CB-209, OCDD and OCDF) showed different trends from those of the lighter ones. The general tendencies of the three types of POPs in soils were consistent with those reported in other studies in this area. The results implied that the enhanced regulations and centralized dismantling action introduced in 2005 might exert a limited influence on these three types of POPs in soils during the sampling period.

Chiral Chemicals as Tracers of Atmospheric Sources and Fate Processes in a World of Changing Climate

Elimination of persistent organic pollutants (POPs) under national and international regulations reduces "primary" emissions, but "secondary" emissions continue from residues deposited in soil, water, ice and vegetation during former years of usage. In a future, secondary source controlled world, POPs will follow the carbon cycle and biogeochemical processes will determine their transport, accumulation and fate. Climate change is likely to affect mobilisation of POPs through e.g., increased temperature, altered precipitation and wind patterns, flooding, loss of ice cover in polar regions, melting glaciers, and changes in soil and water microbiology which affect degradation and transformation. Chiral compounds offer advantages for following transport and fate pathways because of their ability to distinguish racemic (newly released or protected from microbial attack) and nonracemic (microbially degraded) sources. This paper discusses the rationale for this approach and suggests applications where chiral POPs could aid investigation of climate-mediated exchange and degradation processes. Multiyear measurements of two chiral POPs, trans-chlordane and α-HCH, at a Canadian Arctic air monitoring station show enantiomer compositions which cycle seasonally, suggesting varying source contributions which may be under climatic control. Large-scale shifts in the enantioselective metabolism of chiral POPs in soil and water might influence the enantiomer composition of atmospheric residues, and it would be advantageous to include enantiospecific analysis in POPs monitoring programs.

Application of System Dynamics technique to simulate the fate of persistent organic pollutants in soils

Persistent organic pollutants (POPs) are within the most dangerous pollutants released into the environment by human activities. Due to their resistance to degradation (chemical, biological or photolytic), it is critical to assess the fate and environmental hazards of the exchange of POPs between different environmental media.System Dynamics enables to represent complex systems and analyze their dynamic behavior. It provides a highly visual representation of the structure of the system and the existing relationships between the several parameters and variables, facilitating the understanding of the behavior of the system. In the present study the fate of γ-hexachlorocyclohexane (lindane) in a contaminated soil was modeled using the Vensim® simulation software.Results show a gradual decrease in the lindane content in the soil during a simulation period of 10years. The most important route affecting the concentrations of the contaminant was the biochemical degradation, followed by infiltration and hydrodynamic dispersion. The model appeared to be highly sensitive to the half-life of the pollutant, which value depends on environmental conditions and directly affects the biochemical degradation.