Diquat and Copper-ion Residues in Salmon-spawning Channel

Abstract

A mixture of diquat [6,7-dihydrodipyrido(1,2-α: 2′,1′-c) pyrazinediium ion] and copper sulfate pentahydrate was applied to artificial chinook salmon (Onchorhynchus tshawytschaWal.) spawning channels to reduce excessive growths of algae [Cladophora glomerata(L.) Kutz]. Juvenile salmon were not harmed by the applications. A concentration of 100 ppb w/w diquat plus 150 ppb copper-ion was maintained for 3 hr. The alga was controlled satisfactorily for distances up to 0.5 km per treatment. Each treatment consisted of one to three applications, each made on consecutive days. Water temperature was 11.2 C during three winter applications and 15.5 C during a spring application. Diquat was rapidly sorbed out of the treated water to 3.8 ppb at 1.6 km. Copper-ion residues dissipated to 60 ppb at 1.6 km.

Review of Methods to Repair and Maintain Lithophilic Fish Spawning Habitat

“…Chemical treatments can be used to reduce nuisance levels of aquatic plants and filamentous algae, although their use necessitates a cost-benefit analysis and consideration for non-target effects. A combination of diquat and copper sulfide effectively removed Cladophora overgrowth in an artificial salmonid spawning channel off the Sacramento River in California, USA, although associated mortality rates of fish embryos and fry were not reported [63]. However, later chemical treatments using acrolein compounds in the canal resulted in massive fish kills and were discontinued [62].…”