A first assessment of glyphosate, 2,4-D and Cry proteins in surface water of South Africa

Abstract

Agriculture plays a vital role in the South African economy, as well as in the production of maize for food. Genetically modified maize is transformed to encode for crystalline (Cry) proteins found in Bacillus thuringiensis (Bt) and is referred to as Bt maize. Ingestion of specific Cry proteins causes the death of target insects that cause harm to maize plants. Bt crops, along with herbicides such as glyphosate and 2,4-dichlorophenoxyacetic acid (2,4-D), are widely adopted as part of the South African farming regime that aims to increase crop yield and reduce costs of production. As chemical compounds used in agriculture often end up in water sources, their presence should be monitored. There are many such monitoring programmes worldwide, but not in South Africa. We screened surface water sources in a maize-dominated agricultural area in the North West Province in South Africa for the presence of Cry1Ab, glyphosate and 2,4-D using enzyme-linked immunosorbent assays (ELISAs). Cry1Ab was not detected at any site; glyphosate was below the limit of detection at most of the sites but one sample had quantifiable traces of glyphosate; and 2,4-D was detected at all the sites. The concentrations of 2,4-D exceeded those for drinking water according to European guidelines, thus highlighting the need for regular monitoring of these compounds. Many people depend on untreated water resources, which may be contaminated by toxic agricultural chemicals. This report is the first on levels of these target compounds in South African water systems.

Agrochemicals in freshwater systems and their potential as endocrine disrupting chemicals: A South African context

“…This highlights the absence of a regulatory framework for pesticide pollution in South African water ( London et al 2005 ). Moreover, although Dabrowski (2015) developed pesticide-use maps for South Africa, these maps only provide information about 206 active ingredients currently used in the country’s agricultural sector—only 41% of the 500 registered active ingredients ( Horn et al , 2019 ). Unfortunately, knowledge gaps about the majority of current-use pesticides in South Africa, as well as the country’s poorly developed pesticide monitoring and control infrastructure ( Ansara-Ross et al , 2012 ), make assessing their ecotoxicological risks challenging.…”

“…In addition to OCPs and triazine herbicides, the use of other pesticides (glyphosate-based herbicides (GBHs), 2,4-dichlorophenoxyacetic acid (2,4-D), organophosphate insecticides) in South Africa should also be cautioned. These are current-use pesticides which have been detected in the environment ( Morgan et al , 2008 ; Rendón-Von Osten and Dzul-Caamal, 2017 ; Horn et al , 2019 ). Glyphosate [ N -(phosphonomethyl)glycine] is the active ingredient in many non-selective herbicide formulations used globally for the control of weeds ( Daouk et al , 2013 ).…”

“…Glyphosate-based herbicides are also the most commonly applied type of herbicide in South Africa ( Mensah et al , 2013 ) and formulations have various trade names, including the well-known Roundup. In 2012, an estimated 23 million litres of GBHs were sold in South Africa alone ( Horn et al , 2019 ). Although GBHs are widely used throughout South Africa, Horn et al (2019) were the first to report on the levels of glyphosate, 2,4-D and Cry proteins from Bt maize in South African water systems ( Table 1 ).…”

“…In 2012, an estimated 23 million litres of GBHs were sold in South Africa alone ( Horn et al , 2019 ). Although GBHs are widely used throughout South Africa, Horn et al (2019) were the first to report on the levels of glyphosate, 2,4-D and Cry proteins from Bt maize in South African water systems ( Table 1 ). Although glyphosate could only be quantified at one of the sampling locations, this preliminary assessment highlighted the importance of regularly monitoring the presence of pesticides in surface waters.…”

“…Another commonly used pesticide is the broad-spectrum herbicide, 2,4-D, which is used pre- or post-emergence to control broadleaf weeds. It was introduced in the 1940s during World War II ( Hayes and Hansen, 2017 ) and is still used in many countries today, including South Africa, to reduce crop losses ( Horn et al , 2019 ). Islam et al (2018) recently critically reviewed the potential impact of 2,4-D on humans and the environment focusing on its environmental accumulation, interaction with soil, the movement to non-target areas via leaching, volatilisation and drift, and effect on living organisms (fish, amphibians, insects, earthworm, rodents, bacteria) and plants (terrestrial and aquatic).…”