ABSTRACT
Comprehensive air and surface soil monitoring was conducted for new and legacy organochlorine pesticides (OCPs) to fill the knowledge and data gap on the sources and fate of pesticidal persistent organic pollutants (POPs) in the Sultanate of Oman. DDTs in agricultural soil samples ranged from 0.013 to 95.80 ng/g (mean: 8.4 ± 25.06 ng/g), with a median value of 0.07 ng/g. The highest concentration was observed at Shinas, where intensive agricultural practice is prevalent. The dominance of p,p'-DDT in soil and air reflected technical DDT formulation usage in Oman. Among newly enlisted POPs, pentachlorobenzene had the maximum detection frequency in air (47%) and soil (41%). Over 90% of sites reflected extensive past use of hexachlorobenzene. Major OCP isomers and metabolites showed net volatilisation from the agricultural soil, thereby indicating concurrent emission and re-emission processes from the soil of Oman. However, the cleansing effect of oceanic air mass is the possible reason for relatively lower atmospheric OCP levels from a previous study. Although DDT displayed maximum cancer risk, the level is below the permissible limit. DDT primarily stemmed from obsolete stock and inadequate management practices. Hence, we suggest there is a need for DDT regulation in Oman.
ABSTRACT
The buffering of phosphorus concentrations in soil solution by the soil-solid phase is an important process for providing plant root access to nutrients. Accordingly, the size of labile solid phase-bound phosphorus pool and the rate at which it can resupply phosphorous into the dissolved phase can be important variables in determining when the plant availability of the nutrient may be limited. The phosphorus labile pool (Plabile) and its desorption kinetics were simultaneously evaluated in 10 agricultural UK soils using the diffusive gradients in thin-films (DGT) technique. The DGT-induced fluxes in the soil and sediments model (DIFS) was fitted to the time series of DGT deployments (1-240 h), which allowed the estimation of Plabile, and the system response time ( Tc). The Plabile concentration was then compared to that obtained by several soil P extracts including Olsen P, FeO-P, and water extractable P, in order to assess if the data from these analytical procedures can be used to represent the labile P across different soils. The Olsen P concentration, commonly used as a representation of the soil labile P pool, overestimated the desorbable P concentration by 6-fold. The use of this approach for the quantification of soil P desorption kinetic parameters found a wide range of equally valid solutions for Tc. Additionally, the performance of different DIFS model versions working in different dimensions (1D, 2D, and 3D) was compared. Although all models could provide a good fit to the experimental DGT time series data, the fitted parameters showed a poor agreement between different model versions. The limitations of the DIFS model family are associated with the assumptions taken in the modeling approach and the three-dimensional (3D) version is here considered to be the most precise among them.
