Toxicity of phenyl mercuric compounds in California soils

Abstract does not appear. First page follows.

Introduction

In the spring of 1947 the Rhode Island Experiment Station announced that phenyl mercuric acetate (soluble), which had been applied to soil as a fungicide, also controlled crabgrass (Digitaria sp.) seedlings in lawns (1947).4(DeFrance (1947)) reported good control of crabgrass seedlings from seven applications of the commercial product, sold under the trade name of Tat-C-Lect, made at the rate of one pint of concentrate to 100 gallons of water and applied at the rate of 10 gallons per 1,000 square feet. The commercially recommended dosage is eight ounces per gallon, applied twice, five to seven days apart, at a rate of one gallon per 500 square feet.

Because crabgrass is one of the worst of lawn weeds, the commercial publicity given to its control by the phenyl mercuric compounds was very widespread. To determine the eventual toxicity of spray residues in the soil and the possibilities of ridding the soil of their effects was therefore important.

Materials and Methods

Tests were carried out in the greenhouse to study the toxicity, distribution (percolation), and leaching of phenyl mercuric compounds in samples from four California soil series: Yolo, Aiken, Hanford, and Willows. Three compounds were studied in their effects on the soils: phenyl mercuri triethanol ammonium lactate, phenyl mercuric acetate, and phenyl mercuric hydroxide. Kanota oats were used as indicator plants.

Toxicity Tests. The method followed in these tests was first described by (Crafts (1935)). Several series of cultures were grown in unperforated no. 2 cans. They contained the following concentrations of phenyl mercuric compounds: 0.0, 5.0, 15.0, 40.0, 80.0, 140.0, 220.0, 340.0, 490.0, and 680.0 p.p.m., air dry soil basis.

Because of the somewhat low solubility in water of phenyl mercuric acetate, no cultures using this herbicide above 370.0 p.p.m. were set up. The amounts of chemical were taken from a stock solution, diluted to a total volume sufficient to bring the soil to its field capacity, and added in three increments to obtain more even distribution. The cans were then seeded and the soil brought regularly to its field capacity by weighing. After 30 days, the crop was cut at ground level and its fresh weight recorded. It was then returned to each individual culture. The soil, which had dried out over a period of 30 days, was pulverized, poured back into the cans on top of the dried plant material, moistened to its field capacity, and reseeded to determine any change in toxicity.