Impact of Hydrogen Peroxide and Copper Sulfate on the Delayed Release of Microcystin

Arash Zamyadi,Eric C Wert,Craig Adams,Katherine E Greenstein,Erik Rosenfeldt,Caitlin M Glover

doi:10.3390/w12041105

Abstract

Algicides, like hydrogen peroxide and copper sulfate, are commonly applied to recreational waters and drinking water sources to mitigate cyanobacterial blooms. In this work, the effects of hydrogen peroxide and copper sulfate were evaluated in two natural bloom samples (collected from Canadian and American waterbodies) and one lab-cultured Microcystis aeruginosa suspended in Colorado River water. Five algicide to dissolved organic carbon (DOC) dose ratios were evaluated during an initial exposure period of 24 h. One dose ratio (0.4 H2O2:DOC or 0.25 CuSO4:DOC) was then evaluated during stagnation after quenching (hydrogen peroxide) or extended exposure (copper sulfate) for up to 96 or 168 h. During the initial hydrogen peroxide exposure, the CA bloom had no release of intracellular microcystins (MCs) and the USA bloom only released MC at 4 H2O2:DOC. The reverse occurred with copper sulfate, where the CA bloom released MCs at 0.6 CuSO4:DOC but the USA bloom had no detectable extracellular MCs. Extracellular MC was released from the lab-cultured Microcystis at the lowest hydrogen peroxide and copper sulfate doses. In the hydrogen peroxide stagnation experiment, intracellular MC decreased in the USA bloom after 168 h despite the low dose applied. Similarly, the extended copper sulfate exposure led to intracellular MC decreases in both bloom samples after 168 h, despite showing no impact during the initial 24 h monitoring period. The lab-cultured Microcystis was again less resistant to both algicides, with releases observed after less than 2 h of stagnation or exposure. The damage to cells as measured by pigments during these experiments did not match the MC data, indicating that blooms with depressed pigment levels can still be a risk to nearby drinking water sources or recreational activities. These results provide insight on the timeline (up to one week) required for monitoring the potential release of MCs after algicide application.

Highlights

Climate change and human activities have increased the occurrence and severity of cyanobacterial blooms in surface waters used for drinking water, agriculture, and recreation [1,2,3,4]
A limited number of water quality parameters were collected for the three cyanobacterial suspensions prior to algicide exposure
The goals were to determine the doses of hydrogen peroxide and copper sulfate necessary for the release of intracellular MC following a 24 hour exposure period and understand the effect that stagnation time after exposure or extended exposure

Summary

Introduction

Climate change and human activities have increased the occurrence and severity of cyanobacterial blooms in surface waters used for drinking water, agriculture, and recreation [1,2,3,4]. These blooms represent a threat to both ecological and human health when present in surface waters as a result of the biomass and the release of harmful intracellular metabolites, i.e., cyanotoxins [5,6]. As a result of the potential human health effects of MCs, many regulatory bodies have implemented health advisories for drinking and recreational waters. Recreational water guidelines are less stringent, i.e., MC-LR limits of 20 [15] and 8 μg/L [16]

Objectives

Results

Conclusion