Darrell W. Nelson

The decomposition of phthalate esters in soil

Abstract Factors affecting the decomposition of carboxyl‐labelled (14C) phthalic acid (PA), monobutyl phthalate (MBP), and dibutyl phthalate (DBP) were studied in soil incubation experiments conducted under labortory conditions. A lag phase of 10 to 20 days occurred before soil microbes initiated metabolism of MBP and DBP while PA was rapidly decomposed. Approximately 90% of DBP added to soils at rates of 0.1 to 0.4% was decomposed within 80 days under both aerobic and anaerobic conditions. Decomposition of DBP was enhanced in soils by increasing soil pH from 5.2 to 7.0, by adding organic matter, and by elevating the temperature from 23°C to 30°C. Varying soil characteristics and the simultaneous addition of ammonium, CaCO3 or sewage sludge had little effect on the rate or extent of DBP degradation. The addition of DBP in sewage sludge or other waste materials to soils should not pose a long‐term persistence problem.

EFFECTIVENESS OF PHOSPHOROAMIDES IN RETARDING HYDROLYSIS OF UREA SURFACE-APPLIED TO SOILS WITH VARIOUS pH AND RESIDUE COVER1

A field experiment compared the ability of several phosphoroamide compounds to retard urea hydrolysis on a fallowed notill (NT) and conventionally tilled (CT) silt loam soil (pH 5.70). Treatments consisted of urea prills (200 kg N ha-1) with and without inhibitors (4.0 kg ha-1) and a no-fertilizer check. Fertilizers were surface-applied to 10-cm-diameter polyvinyl chloride (PVC) cylinder microplots partially embedded in the soil. Duplicate microplots were removed at intervals after fertilization and analyzed for the quantity of urea remaining. Results indicate that, of the compounds tested, phenyl phosphorodiamidate (PPD) most effectively inhibited urea hydrolysis. Addition of PPD reduced the initial (first 4 to 10 d after fertilization) rate of hydrolysis by 60 to 70% in three of four trials conducted. A laboratory study conducted on a soil at two contrasting initial pH values (5.6 and 7.4) showed that PPD was more effective in the acidic than in the alkaline soil. Two other inhibitors (UI4 and UI5) retarded hydrolysis to a greater degree than did PPD in the alkaline soil. In the same laboratory study phosphoroamide (UI6), not tested in the field, was found to be least effected by soil pH and showed promise as a urease inhibitor in both acidic and alkaline soils. Field and laboratory studies indicate that urea was hydrolyzed 2.3 to 3 times faster when added to corn-residue-covered surfaces than to bare soil. This finding suggests that the residue contained high levels of urease activity.

Changes in phosphorus concentrations in a eutrophic lake as a result of macrophyte-kill following herbicide application

Phosphorus (P) concentrations in water and sediment of a highly eutrophic lake were monitored before and after application of diquat to control the macrophyte Potamogeton crispus. Only a relatively small and short-term increase in P concentration in water occurred shortly after plant die-off resulting from herbicide application. Phosphorus concentrations in shallow water sediments decreased during the summer, and those in deep water sediments increased. Although a large increase in P concentration in the water occurred in late summer, it was not attributed to diquat. No major secondary effects of herbicide application were found during this study.

The effects of heavy metals on microbial biomass in sediments of Palestine Lake

Effects of metal contamination on microbial biomass in sediment samples from three areas in Palestine Lake (one area highly polluted with chromium, cadmium and zinc) were determined. Adenosine triphosphate (ATP) concentrations, determined by the luciferin-luciferase bioluminescent technique, and microbial colony numbers on pour plates were used as biomass indicators. Plate counts showed a significant (P < 0.01) site effect with the highly contaminated area having an order of magnitude lower microbial population than the control area. ATP concentrations also indicated lower microbial biomass in contaminated sediments. The metal concentrations of the most contaminated area averaged 17,840 µg Zn/g, 4380 µg Cr/g and 585 µg Cd/g based on dry weight of sediments. A suppression of organic decomposition was evident in the impacted area; high metal levels and resultant low microbial biomass may have been causative.