10 / 2023-12-16 04:14:38

Diffusion-Advection Process Modeling of Organochlorine Pesticides in Tucutunemo River, Venezuela

Diffusion,Advection,organochlorine pesticides

This paper deals with the diffusion-advection process modeling of organochlorine pesticides (OCPs) dissolved in water of Tucutunemo river, Venezuela. Water samples were captured in the middle of each cross section of the river. Each captured water sample was composed, taking aliquots to fill a container of 1 liter capacity during a sampling time of 8 hours; while the irrigation of agricultural plots was being applied. Samples were collected with a frequency of every six months, in two seasons: dry (April) and rainy (October) during the period 2013-2016. The analytic determination of OCPs was carried out in the Environmental Quality Laboratory of the Ministry of Ecosocialism. A SHIMADZU GC-14B gas chromatograph with capillary column equipped with electronic capture detector was used to determine and quantify analytes. OCPs involved were DDTs (p.p’-DDT, o.p’-DDT, p.p’-DDD, p.p’-DDE, o.p’-DDE) and DRINs  (Aldrin, Dieldrin and Endrin). Four scenarios for simulating the OCPs transport are proposed: 1) molecular diffusion, 2) biochemical transformation, 3) advection-diffusion 4) advection-diffusion with biochemical transformation and sorption/desorption processes. Among DDTs dissolved in water of Tucutunemo river, p.p’-DDT occurred in a permanent concentration of 0.008 mg/L during period 2013-2016, increasing its concentration to close to 0.02 mg/L for the dry season (October 2013-2015).  The change rate of DDTs resulted in a variation of less than 0.001 mg/L, being steady between monitoring stations (MS1 and MS2), while it varied between positive and negative between MS2 and MS3. The DRINs (Aldrin, Dieldrin and Endrin), showed a variable trend between climatic seasons in the period 2013-2016.  In the diffusion-advection modeling, the OCPs molecular diffusion coefficient in the scenario 1 was the highest with respect to scenario 3 and scenario 4. This fact can be explained because of the weighting achieved for each one of processes involved in the estimation of the substrate concentration in the outlet of river reach. In scenario 2, the reaction rate constant K associated to activity by the microorganisms was equivalent to the reaction rate in the mathematical expressions derived by the trickling filters along the deep of trickling filter, which was due to the influence found in the molecular diffusion process, advection with respect to the biochemical transformation. Best performance of substrate concentration in outlet of river reach was obtained with scenario 4, where physical processes (molecular diffusion and advection) were combined with the biochemical transformation.