Sunny Y. Szeto

Distribution of endosulfan residues in the drainage waterways of the Lower Fraser Valley of British Columbia

Abstract Farm ditches flowing into three rivers important to fisheries in the Lower Fraser Valley of British Columbia, Canada, were sampled periodically at seven locations from July to December in 1991, to determine the distribution of total residues of endosulfan (END) including endosulfan sulfate, in ditch water and sediment. Residues of END were detected at levels ranging from 7 ‐7,825 μg/kg in crop soils collected close to the sites for sampling ditch water and sediments. END concentrations in ditch water varied from 0.01 μg/L to 13.4 μg/L, whereas those in ditch sediments ranged from 5 μg/kg to 2,461 μg/kg. Of the two stereoisomers monitored, the concentration of endosulfan II (ENDII) was detected at 8, 7 and 6 times higher than endosulfan I (BNDI) in soils, sediments and water, respectively. The transformation product, endosulfan sulfate (ENDS) was also found in the three substrates, with mean concentrations of 1, 015 μg/kg, 218 μg/kg, and 0.30 μg/L for soils, sediments and water, respectively. The ...

Organophosphorus insecticide residues in farm ditches of the Lower Fraser Valley of British Columbia

Abstract Farm ditches flowing into three important rivers in the Lower Fraser Valley of British Columbia, Canada, were sampled periodically at seven locations from July to December in 1991, to determine the occurrence and levels of seven organophosphorus (OP) insecticides. Based oh sales records for the year, the uses of OP insecticides in this area were as follows: malathion > diazinon > parathion > dimethoate > azinphos‐methyl > fensulfothion, but no sales of chlorfenvinphos. Residues of parathion, diazinon, fensulfothion, dimethoate and chlorfenvinphos were detected at levels ranging from 1 ‐ 7,785 >μg/kg in cropped soils collected from areas adjacent to the sites for sampling ditch water and sediments. Malathion and azinphos‐methyl were not detected in any of the substrates studied, demonstrating their rapid degradation in the environment. Diazinon and dimethoate were consistently found in ditch water at seven locations, with an average concentration of 0.07 μg/L and 0.27 μg/L, respectively. Fensulfot...

Inhibition of brain ache in brook trout by aminocarb and its toxic metabolites

In-vitro inhibitions of brain AChE in brook trout, Salvelinus fontinalis (Mitchill), by aminocarb (4-dimethylamino-m-tolyl N-methylcarbamate) and its toxic metabolites, MAA (4-methylamino-m-tolyl N-methylcarbamate), AA(4-amino-m-tolyl N-methylcarbamate), MFA (4-methylformamido-m-tolyl N-methylcarbamate) and FA (4-formamido-m-tolyl N-methylcarbamate) were investigated. The molar concentrations of inhibitors causing 50% inhibition (I50s) were AA (3.62 X 10(-6] less than MAA (7.92 X 10(-6] less than aminocarb (1.01 X 10(-5] less than MFA (4.29 X 10(-5] less than FA (7.11 X 10(-5]. After exposure of fish to various concentrations of aminocarb (25, 250 and 2500 ppb) and MAA (25, 250, 500 and 2500 ppb) at 9 degrees C in dechlorinated tap water for 96 h, inhibitions of brain AChE ranged from 13 to 77%. Mortality occurred only in fish exposed to 500 ppb (22%) and 2500 ppb (100%) of MAA. Enzyme activities recovered to the control levels 12 to 96 h after the fish had been transferred to clean water for clearing; in survivors of the 500-ppb MAA exposure, however, AChE activities decreased again thereafter.

Comparative hersistence of chlorpyrifos in a mineral soil after granular and drench applications

Abstract Lorsban 15G (15% chlorpyrifos) at 1.6 and 2.2 g a.i./10 m row, and Lorsban 4E (40.7% chlorpyrifos) at 2.0 g a.i./10 m row were applied respectively to a silt loam soil as a band treatment at seeding and as a drench after seeding. The rate of disappearance of chlorpyrifos [Q,Q‐diethyl Q‐(3,5,6‐trichloro‐2‐pyridinyl) phosphorothioate] was relatively fast in the first 15 days but slowed down considerably thereafter regardless of the methods of application and application rates; and there was a statistically significant (p=0.05) linear relationship between the natural logarithm of chlopyrifos concentration and time. Based on the linear regression equations, the calculated pseudo‐first‐order rate constants were 0.041 day‐1 and 0.044 day‐1 respectively for the band treatments at 1.6 and 2.2 g a.i./10 m row; and 0.040 day‐1 for the drench. The calculated half‐lives for all three treatments were similar and they ranged frcm 15.8 days to 17.3 days. The degradation product 3,5,6‐trichloro‐2‐pyridinol (TP) ...

Disappearance of dimethoate, methamidophos and pirimicarb in lettuce.

Foliar sprays of dimethoate at 150 or 300 g a.i./ha, methamidophos at 450 or 900 g a.i./ha and pirimicarb at 140 or 280 g a.i./ha were applied for control of the green peach aphid, Myzus pericae (Sulzer), and the lettuce aphid, Nasonovia ribisnigri ( Mosley ), about 2 weeks before the lettuce started heading, and again about 1 week from harvest. In lettuce, dimethoate partially oxidized to its oxon and pirimicarb converted to its methylamino- and/or formyl methylamino-analogues. Most residues were present in the outer leaves which were exposed directly to the sprays; only traces of residues were detected in samples of the inner head leaves. Total residues disappeared rapidly. Pirimicarb was the least persistent and only traces of residues (less than 0.01 ppm) were detected in marketable heads. Concentrations of dimethoate, including the oxon and of methamidophos were well below their respective tolerances of 2 and 1 ppm respectively.

The degradation of disulfoton in lettuce after applications for control of the lettuce aphid, Nasonovia ribisnigri (Mosley)

Abstract Disulfoton was evaluated as a control agent against the lettuce aphid, Nasonovia ribisnigri (Mosley). Band treatments at 0.9 and 1.9 kg a.i./ha and soil drench treatments at 1.1 and 2.3 kg a.i./ha applied to an organic muck soil at seeding were ineffective whereas foliar sprays at 1.0, 2.0 or 4.0 kg a.i./ha gave effective control. Disulfoton oxidized rapidly in lettuce to its sulfoxide (DSO), sulfone (DSO2), oxygen analogue sulfoxide (DOASO) and oxygen analogue sulfone (DOASO2). The oxygen analogue (DOA) was never detected. When applied as a band treatment or a soil drench, considerable amounts of residues of disulfoton and its toxic metabolites were detected in young plants by the first sampling date 22 days after seeding, but then decreased to less than 0.1 ppm after 36 days. When applied as a foliar spray total residues persisted much longer. They were, however, all below the tolerance of 0.5 ppm in marketable heads.

Degradation of disulfoton, oxydemeton‐methyl, methamidophos and demeton in asparagus plant

Abstract Disulfoton and methamidophos (both at 1.12 kg a.i./ha), oxydemeton‐methyl and demeton, (both at 0.56 kg a.i./ha) were applied as post‐harvest foliar sprays to control the European asparagus aphid, Brachycolus asparagi. Oxidation of disulfoton, oxydemeton‐methyl and demeton to their corresponding sulfoxides and sulfones occurred in asparagus foliage 2 to 5 days after application. The total residues of these three compounds, including their toxic oxidative metabolites declined to less than 0.5 ppm about 47 days after the spray application whereas methamidophos persisted longer; 0.84 ppm of its residue was found even after 85 days. No residue was found above the limit of detection of 0.002 ppm in any asparagus spears which were produced in the following spring; the four compounds were sprayed on the asparagus plants during the previous season at realistic rates for aphid control.