A new system to bioassay pesticides present in the surface microlayer using floating propagules of an aero-aquatic hyphomycetous fungus Pseu doaegerita matsushimae

The surface microlayer often contains pesticides at levels which may be more than one hundred thousand times those sampled in the remainder of the water column. Standard bioassay systems cannot asses these pesticides since no system yet devised has made use of organisms inhabiting the surface microlayer. Using floating propagules of Pseudoaegerita matsushimae, an aeroaquatic hyphomycetous fungus, a bioassay system was devised in which the percentage germinations of such propagules after exposure to various levels of pesticides were plotted to produce a dosegermination scale onto which subsequent data could be fitted. The following pesticides and pesticide mixtures were used: PCP; DDT; Methoxychlor; Bis(tributyl)tin Oxide; Malathion; Captan; 1 part PCP/1 part DDT; 2 parts PCP/1 part DDT; 3 parts PCP/1 part DDT; 2 parts DDT/1 part PCP; 3 parts DDT/1 part PCP; 1 part PCP/1 part Methoxychlor; 2 parts PCP/1 part Methoxychlor; 3 parts PCP/1 part Methoxychlor; 2 parts Methoxychlor/1 part PCP; 3 parts Methoxychlor/1 part PCP. The bioassay system revealed increased sensitivity to pesticides and pesticide mixtures which affected respiratory metabolism. Some pesticide mixtures were more effective in inhibiting germination than their individual components while others appeared much less toxic to the propagules than their unassisted components.