Binding of [14 ^C ] Parathion in Soil: A Reassessment of Pesticide Persistence

Abstract

A steady decrease of extractable [14C] parathion residues in soils over a 1-month incubation period was accompanied by an increase of unextractable, bound 14C-labeled residues, resulting finally in total recoveries of extracted plus bound residues of 80 to 87 percent of the applied radiocarbon. Soils containing bound residues were nontoxic to fruit flies. Binding of 14C-labeled residues was related to the activity of soil microorganisms; soil sterilization resulted in a reduction of binding by 58 to 84 percent. Under flooded (anaerobic) conditions, the binding of compounds labeled with 14C doubled, and parathion was reduced to aminoparathion. Reinoculation of sterilized flooded soil fully reinstated the binding capacity. [14C] Aminoparathion was preferentially bound to soil, since its binding within 2 hours was 30 times greater than that of [14C] parathion. Because of the existence of formerly "unseen," unextractable residues, the concept of "persistent" and "nonpersistent" pesticide residues might have to be reconsidered.

Studies on dissipation and degradation of 14C-ddt and 14C-dde in Pakistani soils under field conditions

“…This may be related to the different nature of soils. The slow build-up of bound pesticide residues with time has been reported by Katan et al, 1976. To determine if DDT was degraded in soil, the methanol extractable 14 C-residues were qualitatively and quantitatively determined by gas liquid chromatography.…”

Accelerated Mineralization of Two Organophosphate Insecticides in the Rhizosphere

“…Whereas it has been shown that p-nitrophenol can be mineralized by P. aeruginosa after its liberation from parathion by P. stutzeri in a chemostat system (4), and the same association showed a promise for the accelerated degradation of parathion in contaminated soils (5), reductive pathways lead to the formation of aminoparathion and p-aminophenol (15,19). According to a recent report (11), the latter compound can become stabilized as soil-bound residue. Because of the position of the "4CO2 label, our experiments do not indicate whether the metabolisam in the rhizosphere favors or discourages the formation of such soilbound residues.…”

Soil-Bound Residues

“…Reduced mobility and biocidal activity due to bonding to humic substances are often described (5)(6)(7)(8). It is in some cases supported by various experimental results, that parent molecules or metabolites are bound to the humic matrix either by covalent bonding (9)(10)(11)(12)(13)(14)(15)(16)51), ionic bonding (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28), charge transfer complexes (29)(30)(31)(32)(33), ligand exchange (34,35), hydrogen bonding (23,31,(36)(37)(38)(39)(40), van der Waals forces (22,(41)(42)(43)(44), hydrophobic sorption (45)(46)(47)(48)(49)…”

“…As recently discussed (82), innovatively applied analytical methods like silylation of soil organic matter constituents, solid-phase microextraction, thermodesorption, pyrolysis-GC-MS and sophisticated bioassays will broaden the insight into the field of bound residue research. The combination of analytical approaches with the use of stable and radioactive isotope labelling techniques ( 12 C, 13 C, 14 C, 15 N, 31 P) can be extremely advantageous in this respect. In addition, aspects of soil biology in relationship to soil organic matter turnover can be addressed and may contribute to enlarge the knowledge in this field, respectively.…”