Copper-Based Aquatic Algaecide Adsorption and Accumulation Kinetics: Influence of Exposure Concentration and Duration for Controlling the Cyanobacterium Lyngbya wollei

Abstract

Filamentous mat-forming cyanobacteria are increasingly impairing uses of freshwater resources. To effectively manage, a better understanding of control measures is needed. Copper (Cu)-based algaecide formulations are often applied to reactively control nuisance cyanobacterial blooms. This laboratory research assessed typical field exposure scenarios for the ability of Cu to partition to, and accumulate in Lyngbya wollei. Exposure factors (Cu concentration × duration) of 4, 8, 16, 24, 32 h were tested across three aqueous Cu concentrations (1, 2, 4 ppm). Results indicated that internally accumulated copper correlated with control of L. wollei, independent of adsorbed copper. L. wollei control was determined by filament viability and chlorophyll a concentrations. Similar exposure factors elicited similar internalized copper levels and consequent responses of L. wollei. Ultimately, a "concentration-exposure-time" (CET) model was created to assist water resource managers in selecting an appropriate treatment regime for a specific in-water infestation. By assessing the exposure concentration and duration required to achieve the internal threshold of copper (i.e., critical burden) that elicits control, water management objectives can be achieved while simultaneously decreasing the environmental loading of copper and potential for non-target species risks.

Evaluation of copper dissipation, exposure factor, and algaecidal efficacy in an irrigation canal following pulse ‘slug’ application of a chelated copper algaecide

“…Copper sulfate has a sorption and depuration profile that is expected to rapidly move to the algae but not effectively internalize for algaecidal effects (Bishop 2016). The sorption kinetics observed by Bishop et al (2017) in short exposures indicate Captain XTR to have increased ability to penetrate into nuisance algae and achieve internal control thresholds, and are not solely driven by active transport from externally sorbed copper. Interactivity of copper from copper sulfate with water chemistry (e.g., alkalinity; Meyer 1999) and algal cells (Crist et al 1990) is predicted to rapidly remove copper mass.…”

“…Surfactants and adjuvants further can increase this interaction with the algal cell and assist in internal transfer (Closson and Paul 2014;Ullah et al 2015). Bishop et al (2017) found pulsed exposures (1-4 h) of Captain XTR can be effective at controlling a nuisance mat-forming algae, although require a proportional increase in concentration at lower durations (i.e., exposure factor). Chelated copper provides more rapid copper internalization than copper sulfate and should be highly considered in short duration exposures such as through canal systems (Bishop 2016).…”

“…Dispersion processes in moving water tend to create extended copper exposures at lower peak concentrations. To account for these dynamic exposures encountered by algae at different downstream points, we used a factor exposure assessment where the copper concentration is multiplied by the exposure duration (Bishop et al 2017). These exposure data coupled with efficacy testing according to the mass of algae present (critical burden concept; Bishop and Rodgers 2012;Bishop et al 2015) can provide a framework to predict algaecidal efficacy in a range of canal systems based on site-specific parameters (e.g., algal biomass, type of algae, flow).…”

Controlling Lyngbya wollei in three Alabama, USA reservoirs: summary of a long-term management program

“…Field research with Program 5 in 2013 also supported its effectiveness in applied management programs in these reservoirs . Rapid copper sorption has been documented following Captain XTR exposures, including with short contact times (Bishop et al 2017;Willis et al 2018). The formulation also results in increased internalized copper into L. wollei biomass which is significantly correlated with control (Bishop et al 2018a) and less likely to desorb back into the water (Bishop et al 2018b).…”

Toxic benthic freshwater cyanobacterial proliferations: Challenges and solutions for enhancing knowledge and improving monitoring and mitigation

“…Copper products act on algae by decreasing electron transport in photosystem I, preventing cell division, and inhibiting the enzyme catalase (Stauber & Florence, 1987). Several studies have shown that copper‐based algaecides are successful for the control of benthic algae (Bishop, Lynch, Willis, & Cope, 2017; Bishop, Willis, & Horton, 2015; Calomeni et al, 2018). However, the efficacy of these algaecides depends on several factors, such as the formulation of copper used, initial thickness of the benthic algal mat, overall water quality, and the species composing the mat (Bishop, Richardson, & Willis, 2018; Willis, Pearce, & Bishop, 2018).…”