Herbicide contaminationContinuing with the topic of last week's post on the importance of physical-chemical water treatment , Carolina García, a collaborator on the Official University Master's Degree in Management of Occupational Risk Prevention, Excellence, the Environment and Corporate Responsibility of Bureau Veritas University Center, develops in this new post the case of contamination with herbicides.
The application of herbicides in agricultural soils is an effective and well-established practice to control weed growth in crops.
Phenyl-urea compounds (Figure 1) are the most widely used herbicides in current agriculture . They act by inhibiting photosynthesis and are mainly applied as pre- and post-emergence herbicides for annual weed control.
Figure 1. Chemical structure of phenyl-urea herbicides
Figure 1. Chemical structure of phenyl-urea herbicides
These herbicides have received special attention in recent part time data years due to their toxicity and possible carcinogenic properties , in addition to the fact that it takes weeks or even months to eliminate them from the environment.
Being stable, they remain undegraded in crops or soils and their solubility in water allows them to reach groundwater and surface water sources through washing and leaching processes; therefore, they must be controlled from their direct discharge to their degradation products .
Pollution by pesticides in general, and by herbicides in particular, leads to a series of environmental problems . Pesticides alter the balance of nature by upsetting ecological systems and producing toxic effects for people and animals.
In addition, insects and other parasites themselves develop resistant species, which requires the use of higher doses or more effective products .
In response to this problem, the European Union has established in its Council Directive 98/83/EC a maximum permissible concentration of 0.1 mg /L for each individual pesticide in drinking water , and a concentration of 0.5 mg /L for the total sum of all pesticides (including their metabolites and degradation products), in order to guarantee the essential quality and healthiness in water intended for human consumption, whether groundwater or surface.
In this context, we carried out a research study on the removal of herbicides in different types of drinking water by using physical-chemical methods .
Specifically, we chose four herbicides belonging to the phenyl-urea family , widely used in agriculture, as models of contaminants present in natural waters: isoproturon, chlortoluron, diuron and linuron.
These compounds were dissolved in different types of water (ultra-pure, commercial mineral, underground and surface), in order to simulate treatment processes using different types of physical-chemical processes in real waters contaminated with these herbicides.
In this study, we established the influence of operational variables such as pressure and temperature conditions, pH, initial concentration of oxidizing agents, type of water used and nature of the organic compound.
The physical-chemical treatments were applied to these herbicides , both individually and jointly, these being:
Chemical degradation using oxidizing agents: UV radiation, ozone and advanced oxidation processes, by combining these with hydrogen peroxide and iron (II) ions, known as Fenton's reagent, among others.
Removal by filtration through ultrafiltration (UF) and nanofiltration (NF) membranes, under different operating conditions (Figure 2).
Combined physical-chemical processes , applying ozonation-NF series processes and vice versa.
Basic diagram of a membrane separation process
Figure 2. Basic diagram of a membrane separation process
Results of the case study
Overall, chemical oxidation methods were found to be suitable for removing phenyl-urea herbicides from groundwater and surface water, and were suitable for use in real water treatment plants.