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Introduction

Concentrations of alkyl halide nematicides in soils can be predicted with some certainty at any given point in the soil profile at any given time. (See Part I in this series.) For the most efficient use of these materials, it is then necessary to determine the relationship of dosage to organism response (dosageresponse) and to establish curves based on these data to coincide with the diffusion gradients. As this organismdosage-response data accumulates, eventually we may be able to answer questions pertaining to (1) the increased growth response of plants; (2) the mode of nematicidal action; and (3) pesticide specificity (Bollen, 1961); (Goring, 1962); (Mankau and Imbriani, 1971); (Martin, Baines, and Erwin, 1957).

In this report, the authors sought to establish the above-mentioned curves for several nematodes under laboratory conditions.

Previous work

Techniques for previous dosage-response studies of the nematicides in question have involved (1) known amounts of toxicant added to sealed jars containing soil and associated organisms (Baines, et al. 1966); (Moje, Martin, and Baines, 1957); (2) toxicants dissolved in the water phase and test organisms immersed in the solution (Evans and Thomason, 1971); and (3) cumulative data of various field experiments used to predict the relative toxicity of various chemicals.

However, several problems are inherent with these techniques: For instance, hydrolysis and sorption effects were not sufficiently known—so that the exact concentration to which the organism was exposed could not be determined. Also, in the experiments where nematodes were placed in a solution, chemical may have been lost due to its sorption onto the various materials used to construct the exposure flasks, or from escape through seals. (This last would be especially true with EDB.) Hydrolysis of some compounds can also occur under these conditions.

This study

For the experiments described here, dosages were accurately determined by monitoring the vapor phase concentrations throughout the exposure period (Kolbezen, personal communication). Knowledge of the vapor-phase concentrations and the value for Henry’s constant permitted us to calculate the water phase concentrations.