A Mathematical Model For Hydrophobic Organic Contaminant Uptake By Plant Roots

Polycyclic aromatic hydrocarbons are a class of hydrophobic organic pollutants with carcinogenicity,mutagenicity and toxicity.Studies have shown that at least 90%PAHs in the environment reside in the top soil.Plant uptake of PAHs and PAH-contaminated soil restoration have been of great concern.The uptake mathematical model can predict the risk of environmental pollution and correctly evaluate the pollution of crops.However,the mathematical model including active uptake of PAHs by plant roots is unavailable.Based on the reports of the uptake of organic pollutants by plant roots,this paper established a novel mechanistic model including active and passive transport through the differential equation;discussed the effect of the environmental factors on kinetic parameters;determined the active absorption coefficient and analyzed the model-predicting results of phenanthrene uptake by wheat roots,and preliminarily applied this model to phenanthrene uptake process in garlic roots.The main results obtained are shown as follows:(1)On the basis of active and passive uptake of organic pollutants by plant roots,considered the acropetal translocation of the organics and the dilution of growth and metabolism,a novel mechanistic and mathematical model is built.Model analysis indicates that plant species,types of pollutants and the external environment are the three factors affecting plant uptake of organic pollutants(2)The experimental results show that temperature,pH,and seedling of age have a significant effect on the kinetic parameters.In the range of 15?30?,the Km(Michaelis constant)and Vmax(maximum absorption rate)of phenanthrene uptake by wheat roots are increasing with temperature;at pH 3.00,Km peaks the minimum,at pH5.50,Vmax is the maximum;at the seventh day of the wheat seedling age,the kinetic parameters obtain the maximum.But there is no significant difference in uptake kinetics between in vivo and in vitro wheat roots.(3)The active coefficient is 0.68 for wheat root uptake phenanthrene.By comparison,1 stOpt has a better performance than MATLAB in data fitting,and the prediction by the novel mechanistic model in MATLAB is better than by Trapp's dynamic model.By setting time,we can obtain the longer change of phenanthrene concentration in wheat roots in MATLAB.At about 40 h,the phenanthrene concentration reaches a maximum,and then continue to decrease.(4)The prediction of the novel model used for garlic root is less than the experimental data.But the novel model prediction results possess the same order of magnitude as the experimental data and fulfill the anticipated requirements.But it needs to be further perfected.Taken together,we can conclude that the novel model is able to be employed to predict the uptake of hydroponic organic pollutants.It has an important theoretical and practical significance for the risk assessment of organic pollutants and the practical applications of phytoremediation.