In the present study, analytical solutions are obtained for two-dimensional advection dispersion equation for conservative solute transport in a semi-infinite heterogeneous porous medium with pulse type input point source of uniform nature. The change in dispersion parameter due to heterogeneity is considered as linear multiple of spatially dependent function and seepage velocity whereas seepage velocity is nth power of spatially dependent function. Two forms of the seepage velocity namely exponentially decreasing and sinusoidal form are considered. First order decay and zero order production are also considered. The geological formation of the porous medium is considered of heterogeneous and adsorbing nature. Domain of the medium is uniformly polluted initially. Concentration gradient is considered zero at infinity. Certain new transformations are introduced to transform the variable coefficients of the advection diffusion equation into constant coefficients. Laplace Transform Technique (LTT) is used to obtain analytical solutions of advection-diffusion equation. The solutions in all possible combinations of temporally and spatially dependence dispersion are demonstrated with the help of graphs.

This study derives an analytical solution of a one-dimensional (1-D) Advection-Dispersion Equation (ADE) for solute transport with two contaminant sources incorporating the source term. Groundwater velocity is considered as a linear function of space while the dispersion as a nth power of velocity and analytical solutions are obtained for , and . The solution is derived using the Generalized Integral Transform Technique (GITT) with a new regular Sturm-Liouville Problem (SLP). Analytical solutions are compared with numerical solutions obtained in MATLAB pedpe solver and are found to be in good agreement. The obtained solutions are illustrated for linear combination of exponential input distribution and its particular cases. The dispersion coefficient and temporal variation of the source term on the solute distribution are demonstrated graphically for the set of input data based on similar data available in the literature. As an illustration, model predictions are used to estimate the time histories of the radiological doses of uranium at different distances from the sources boundary in order to understand the potential radiological impact on the general public for such problem.

Mathematical models for pollutant transport in semi-infinite aquifers are based on the advection-dispersion equation (ADE) and its variants. This study employs the ADE incorporating time-dependent dispersion and velocity and space-time dependent source and sink, expressed by one function. The dispersion theory allows mechanical dispersion to be directly proportional to seepage velocity. Initially the aquifer is assumed contaminant free and an additional source term is considered at the inlet boundary. A flux type boundary condition is considered in the semi-infinite part of the domain. Laplace transform technique (LTT) is then applied to obtain a closed form analytical solution. The effect of source/sink term as a function in the one-dimensional advection-dispersion equation is explained through the graphical representation for the set of input data based on similar data available in hydrological literature. Matlab software is used to obtain the graphical representation of the obtained solution. The obtained analytical solution of the proposed model may be helpful in the groundwater hydrology areas.

The aim of this study is to develop analytical solutions for one-dimensional advection-dispersion equation in a semi-infinite heterogeneous porous medium. The geological formation is initially not solute free. The nature of pollutants and porous medium are considered non-reactive. Dispersion coefficient is considered squarely proportional to the seepage velocity where as seepage velocity is considered linearly spatially dependent. Varying type input condition for multiple point sources of arbitrary time-dependent emission rate pattern is considered at origin. Concentration gradient is considered zero at infinity. A new space variable is introduced by a transformation to reduce the variable coefficients of the advection-dispersion equation into constant coefficients. Laplace Transform Technique is applied to obtain the analytical solutions of governing transport equation. Obtain results are shown graphically for various parameter and value on the dispersion coefficient and seepage velocity. The developed analytical solutions may help as a useful tool for evaluating the aquifer concentration at any position and time.

The present study deals with groundwater pollution in multilayer aquifer. The model is based on decomposition of finite layers in semi-infinite groundwater reservoir. A constant pollutant source is injected at the input boundary of the uppermost layer (UML) of the landfill. At the intermediate inlet boundary, some average value for the longitudinal exchange of the input source concentration in each sub-layer is considered from the previous layer. Initially, the aquifer is not solute free in each sub layer that means some constant background contaminant concentration exists. In each sub layer, concentration gradient is assumed to be zero at the extreme boundary. The linear sorption and first orders decay terms are considered to model the groundwater pollution in multilayer aquifer. The Laplace transform technique is adopted to solve one-dimensional (1D) advection-dispersion equation (ADE). This approach is helpful to understand the solute migration in finite sub layers. The results are elucidated for the different time periods to examine the peak of pollutant concentration level in geological formations.

Marine debris has become a major form of pollution and a serious ecosystem health concern. The present study evaluates the accumulation, origin, and fate of debris in intertidal coral habitats of Mumbai-one of the world's highly populated coastal cities on the west coast of India. Predominantly, seven hermatypic coral species belonging to seven genera and five families were identified and mainly represented by Pseudosidastrea, Porites, and Bernardpora. In terms of number, the mean density of marine debris was 1.60 ± 0.13 SE items/m², which is higher than the global average. The mean density of plastic debris was 1.46 ± 0.14 SE items/m². Approximately 9% of total coral colonies were in physical contact with debris, and 22% of these colonies showed visible signs of partial bleaching. Single use plastic bags and wrappers were dominant plastic debris. The study area was characterized as ‘very poor cleanliness’ according to the Beach Quality Indexes, which include the Clean Coast Index, General Index, and Hazardous Items Index. The numerical model indicates the influence of river discharge and probable areas of plastic accumulation with high tidal currents in this region, maneuvering the spatial advection of litter in the nearshore areas. Combined analysis of ground-truthing and model simulation implies that the possible contributing sources of litter were representatives of land-based and sea-originated. The overall results point to increasing anthropogenic stressors threatening coastal coral communities, including marine debris pollution. It is advocated to adopt an integrated coastal zone management approach supported by coordinated policy frameworks could guide the mitigation of the debris footprint in coastal environments.

The identification and quantification of pharmaceutical and personal care products (PPCPs) in aquatic ecosystems is critical to further studies and elucidation of their fate as well as the potential threats to aquatic ecology and human health. This study used mass balances to analyse the sources, transformation, and transport of PPCPs in rivers based on the population and consumption habits of residents, the removal level of sewage treatment, the persistence and partitioning mechanisms of PPCPs, hydrological conditions, and other natural factors. Our results suggested that in an urbanized river of Guangzhou City, China, the daily consumption of PPCPs was the main reason for the variety of species and concentrations of PPCPs. Through the determination of PPCPs in the river water samples and a central composite design (CCD) methodology, the dominant elimination mechanisms of caffeine and carbamazepine from river water were photolysis and biodegradation, but that of triclosan was sorption rather than biodegradation. The mass data of 3 PPCPs were estimated and corroborated using the measured data to evaluate the accuracy of the mass balance. Finally, caffeine, carbamazepine and triclosan discharged from the Shijing River into the Pearl River accounted for 97.81%, 99.52%, and 28.00%, respectively, of the total mass of these three compounds in the surface water of Shijing River. The results suggest that photolysis are the main process of natural attenuation for selected PPCPs in surface waters of river systems, and the transfer processes of PPCPs is mainly attributed to riverine advection. In addition, the low concentration of dissolved oxygen inhibited the degradation of PPCPs in the surface water of Shijing River.

Perfluorooctane sulfonate (PFOS) and related substances are widely used in various industrial and commercial applications in China that ultimately discharge sufficient quantities of PFOS to the environment. It remains unclear how emissions of PFOS ultimately affect its concentrations as well as its fate in the environment. In this study, an improved Berkeley-Trent (BETR) multimedia model is developed to predict the PFOS levels with spatial and temporal distributions on unsteady state mode from 1981 to 2050, by taking the Bohai Rim of China as a case. The results showed that the modeled concentrations agreed well with the measured data. According to the model, PFOS concentrations in fresh water peaked in some months after the peak emission (2008 or 2009), whereas in urban soil the concentrations increased to peak slightly later (around 2014). Among the selected regions, Beijing and Tianjin were simulated with higher PFOS levels in the past and present because of their higher urbanization and industrialization since the 1980s, while in the future, Shandong and Liaoning are expected to have higher concentrations of PFOS than those in Beijing. The water system including coastal water, fresh water and sediment was the biggest sink for PFOS for coastal regions. Among the chemical inputs, direct primary emissions played a more important role, whereas for chemical removal processes, inter-regional advection and background outflow were the predominant pathways. The results would be useful to control the PFOS releases in China and will help the management agencies to implement the “Stockholm Convention” effectively.

Accurate prediction of the colloid-driven transport of radionuclides in porous media is critical for the long-term safety assessment of radioactive waste disposal repository. However, the co-transport and corelease process of radionuclides with colloids have not been well documented, the intrinsic mechanisms for colloids-driven retention/transport of radionuclides are still pending for further discussion. Thus the controlling factors and governing mechanisms of co-transport and co-release behavior of Eu(III) with bentonite colloids (BC) were discussed and quantified by combining laboratory-scale column experiments, colloid filtration theory and advection dispersion equation model. The results showed that the role of colloids in facilitating or retarding the Eu(III) transport in porous media varied with cations concentration, pH, and humic acid (HA). The transport of Eu(III) was facilitated by the dispersed colloids under the low ionic strength and high pH conditions, while was impeded by the aggregated colloids cluster. The enhancement of Eu(III) transport was not monotonically risen with the increase of colloids concentration, the most optimized colloids concentration in facilitating Eu(III) transport was approximately 150 mg L⁻¹. HA showed significant promotion on both Eu(III) and colloid transport because of not only its strong Eu(III) complexion ability but also the increased dispersion of HA-coated colloid particles. The HA and BC displayed a synergistic effect on Eu(III) transport, the co-transport occurred by forming the ternary BC-HA-Eu(III) hybrid. The transport patterns could be simulated well with a two-site model that used the advection dispersion equation by reflecting the blocking effect. The retarded Eu(III) on the stationary phase was released and remobilized by the introduction of colloids, or by a transient reduction in cation concentration. The findings are essential for predicting the geological fate and the migration risk of radionuclides in the repository environment.

Concentrations of polychlorinated biphenyls, polyaromatic hydrocarbons, hexachlorobenzene, and DDE were determined by passive sampling (semipermeable membrane devices) with exposure times of 1–1.5 years at 0.1–5 km depth in the Irminger Sea, the Canary Basin (both North Atlantic Ocean), and the Mozambique Channel (Indian Ocean). The dissipation of performance reference compounds revealed a pronounced effect of hydrostatic pressure on the sampler-water partition coefficients. Concentrations in the Irminger Sea were uniform over the entire water column (0.1–3 km). At the Canary Basin site, concentrations were 2–25 times lower near the bottom (5 km) than at 1.4 km. Concentrations in the Mozambique Channel (0.6–2.5 km) were lower than at the other two locations, and showed a near-bottom maximum. The data suggest that advection of surface waters down to a depth of about 1 km is an important mechanism of contaminant transport into the deep ocean.