Toxicity and Bioavailability of Copper Herbicides (Clearigate, Cutrine-Plus, and Copper Sulfate) to Freshwater Animals

Abstract

In designing aquatic herbicides containing copper, an important goal is to maximize efficacy for target species while minimizing risks for nontarget species. To have a margin of safety for nontarget species, the concentration, duration of exposure (i.e., uptake), and form (i.e., species) of copper used for herbicidal properties should not elicit adverse effects on populations of nontarget species. To determine the potential for risk or adverse effects (conversely the margin of safety), data regarding the comparative toxicity of copper-containing herbicides are crucial. A series of comparative toxicity experiments was conducted, including baseline estimates of toxicity (LC50s, LOECs), sensitive species relationships (thresholds and exposure-response slopes), and bioavailability of toxic concentrations and forms of copper 7 days after initial herbicide application. Aqueous 48-h toxicity experiments were performed to contrast responses of Daphnia magna Strauss, Hyalella azteca Saussure, Chironomus tentans Fabricius, and Pimephales promelas Rafinesque to copper herbicides: Clearigate(R), Cutrine(R)-Plus, and copper sulfate. D. magna was the most sensitive aquatic animal tested for all three herbicides; 48-h LC50s for organisms exposed to Clearigate, Cutrine-Plus, and copper sulfate were 29.4, 11.3, and 18. 9 microg Cu/L, respectively. In terms of potency (calculated from the linearized portion of the exposure-response curves, which included 50% mortality), D. magna was the most sensitive animal tested. Organisms exposed to Clearigate, Cutrine-Plus, and copper sulfate had exposure-response slopes of 2.55, 8.61, and 5.07% mortality/microg Cu/L, respectively. Bioavailability of Clearigate and Cutrine-Plus was determined by comparing survival data (LC50s) of test organisms exposed to herbicide concentrations during the first and last 48-h of a 7-day exposure period. Even in these relatively simplified water-only exposures, a transformation of copper to less bioavailable species over time was observed with a 100-200% decrease in toxicity (i.e., an increase in 48-h LC50s) for all four test animals. This series of laboratory experiments provides a worst-case scenario for determining the risk associated with the manufacturer's recommended application rates of Clearigate (100-1,000 microg Cu/L), Cutrine-Plus (200-1,000 microg Cu/L), and copper sulfate (100-500 microg Cu/L) in natural waters for four nontarget freshwater animals.

Existing and emerging cyanocidal compounds: new perspectives for cyanobacterial bloom mitigation

“…However, it must be considered that the bioavailability of copper after application in aquatic ecosystems is modified by pH, organic carbon, alkalinity, ionic strength, presence of organic (e.g. humic) substances, or conductivity and that the narrow concentration range between general algicidal and the wanted more specific cyanocidal functionality likely limits the selective application of copper as a specific cyanocide (Mastin and Rodgers 2000). It is also considered that the duration of cyanostatical effects of copper in aquatic ecosystems lasts for around 1 week only, which is due to rapid loss from the water phase through precipitation of copper as insoluble salts and hydroxylates (Cooke et al 1993;Zhou et al 2013;Fan et al 2013).…”

Affinity and Efficacy of Copper Following an Algicide Exposure: Application of the Critical Burden Concept for Lyngbya wollei Control in Lay Lake, AL

“…Previous studies indicate that the fundamental aspect of such laboratory experiments should base the exposure on a mass of algicide to mass of algae relationship. Copper algicide formulations can differ significantly in terms of copper partitioning and consequent algicidal efficacy (Stauber and Florence 1987;Mastin and Rodgers 2000;Murray-Gulde et al 2002;Rodgers 2011, 2012). Despite a large fraction of applied copper that may rapidly partition to the algae (Crist et al 1990; Levy et al 2007), the efficiency of a copper formulation and subsequent algal responses are primarily dictated by the amount of applied copper that transfers to internal toxic sites of action (infused; Stauber and Florence 1987;Stauber and Davies 2000;Bishop and Rodgers 2012).…”

“…Despite a large fraction of applied copper that may rapidly partition to the algae (Crist et al 1990; Levy et al 2007), the efficiency of a copper formulation and subsequent algal responses are primarily dictated by the amount of applied copper that transfers to internal toxic sites of action (infused; Stauber and Florence 1987;Stauber and Davies 2000;Bishop and Rodgers 2012). The efficiencies of different copper formulations need to be assessed to identify the formulation that achieves the critical burden (infused copper concentration per mass of algae required to achieve control) with the lowest amounts of applied algicide (Masuda and Boyd 1993;Mastin and Rodgers 2000;Bishop and Rodgers 2012). By measuring the critical burden of the targeted alga to a specific algicide, and quantifying algae mass present at a field site, a specific algicide formulation and corresponding amount to achieve control can be predicted.…”

The combined effect of copper and low pH on antioxidant defenses and biochemical parameters in neotropical fish pacu, Piaractus mesopotamicus (Holmberg, 1887)

“…As described by Aragão et al (2003), the water hardness of most of the Brazilian river basins is low (soft water), which enables toxicity tests to be carried out. According to Mastin and Rodgers (2000) the fast decrease in copper concentration may occur as a consequence of the transference of the cation to other compartments of the system or by the low residence time of CuSO 4 in the water column. The general health conditions of fish were normal throughout the experiments.…”