Acute toxicity of Roundup® herbicide to three life stages of the freshwater shrimp Caridina nilotica (Decapoda: Atyidae)

Abstract

Glyphosate based herbicides, including Roundup®, are frequently used in the chemical control of weeds and invading alien plant species in South Africa. These herbicides ultimately get into water courses directly or indirectly through processes such as drifting, leaching, surface runoff and foliar spray of aquatic nuisance plants. Despite their widespread use, no water quality guideline exists to protect indigenous South African freshwater organisms from the toxic effects of these herbicides. The toxicity of the herbicide Roundup® was assessed using three different life stages of the freshwater shrimp Caridina nilotica, a prevalent species in South African freshwater ecosystems. Neonate (<7days post hatching (dph)), juvenile (>7dph and <20dph) and adult (>40dph) shrimps were exposed to varying concentrations (1.5–50mg/L acid equivalence (a.e.)) of the herbicide in 48 and 96h acute toxicity tests in order to determine the most sensitive life-stage. The results showed neonates to be more sensitive to Roundup® than both juveniles and adults with mean 96h LC50 values of 2.5, 7.0 and 25.3mg/L a.e. respectively. The estimated 96h LC50 of neonates is much lower than the application rate (20–30mg/La.e.), although the application’s impact will depend on the dilution rate of the applied concentration in the environment. All three life-stages of unexposed animals exhibited active and coordinated movement but exposed shrimps were erratic and slow in their movements, with neonates showing most of these behavioral irregularities. This study shows that low levels of the herbicide Roundup® may adversely affect C. nilotica health and survival. Thus, the herbicide should be carefully managed to minimize any negative impact on non-target freshwater organisms.