Fate and Effects of Azinphos-Methyl in a Flow-Through Wetland in South Africa

Abstract

Our knowledge about the effectiveness of constructed wetlands in retaining agricultural nonpoint-source pesticide pollution is limited. A 0.44-ha vegetated wetland built along a tributary of the Lourens River, Western Cape, South Africa, was studied to ascertain the retention, fate, and effects of spray drift-borne azinphos-methyl (AZP). Composite water samples taken at the inlet and outlet during five spray drift trials in summer 2000 and 2001 revealed an overall reduction of AZP levels by 90 +/- 1% and a retention of AZP mass by 61 +/- 5%. Samples were collected at the inlet outlet, and four platforms within the wetland to determine the fate and effect of AZP in the wetland after direct spray drift deposition in the tributary 200 m upstream of the inlet. Peak concentrations of AZP decreased, and the duration of exposure increased from inlet (0.73 microg/L; 9 h) via platforms 1 and 4 to outlet (0.08 microg/L; 16 h). AZP sorbed to plants or plant surfaces, leading to a peak concentration of 6.8 microg/kg dw. The living plant biomass accounted for 10.5% of the AZP mass initially retained in the wetland, indicating processes such as volatilization, photolysis, hydrolysis, or metabolic degradation as being very important AZP was not detected in sediments. Water samples taken along two 10-m transects situated perpendicular to the shore indicated a homogeneous horizontal distribution of the pesticide: 0.23 +/- 0.02 and 0.14 +/- 0.04 microg/L (n = 5), respectively. Both Copepoda (p = 0.019) and Cladocere (p = 0.027) decreased significantly 6 h postdeposition and remained at reduced densities for at least 7 d. In parallel, the chlorophyll a concentration showed an increase, although not significant, within 6 h of spray deposition. The study highlights the potential of constructed wetlands as a risk-mitigation strategy for spray drift-related pesticide pollution.

Urban groundwater quality in sub-Saharan Africa: current status and implications for water security and public health

“…Karlsson et al 2000;Schulz et al 2003;Awofolu and Fatoki 2004), and pesticide storage and use remains largely unregulated and monitored (Dalvie et al 2006;London et al 2005). There are few studies that have investigated micro-organic compounds such as pharmaceuticals in freshwater sources (Hughes et al 2012;Oketola FC faecal coliform (values given as 0 are below detection limit of method), SEC specific electrical conductivity, TC total coliform, TDS total dissolved solids.…”

Impacts of particulate organic carbon and dissolved organic carbon on removal of polycyclic aromatic hydrocarbons, organochlorine pesticides, and nonylphenols in a wetland

“…Until now, available information on the performance of wetlands is mainly about general contaminant parameters, such as BOD 5 , nitrate nitrogen, and ortho-phosphate (U.S. EPA 1993; Belmont and Metcalfe 2003;Bezbaruah and Zhang 2003). However, some recent studies have focused on specific organic contaminants such as herbicides, pesticides, and pharmaceutical and personal care products (Matamoros et al 2005(Matamoros et al , 2007(Matamoros et al , 2008Matamoros and Bayona 2006;Schulz and Peall 2001;Schulz et al 2003;Rose et al 2006). Those studies highlighted the potential of wetlands as a risk-mitigation strategy for many water bodies polluted by organic contaminants.…”

“…Therefore, the removals or fates of organic contaminants in wetlands are the consequences of the two processes. Individual contaminants tend to interact with sediments, suspended particulates, water, and biota (transport processes) (Smit et al 2008;Weber et al 2006;Zhou and Maskaoui 2003) and be chemically and biologically transformed (Schulz et al 2003;Gross et al 2004) to different extents due to physicochemical properties such as vapor pressure, solubility, hydrophobicity, and biodegradability. Consequently, transport, transformation and fates of organic contaminants in wetlands greatly depend on their physicochemical properties.…”

Pesticide behavior in modified water-sediment systems

“…40) About a 10% residue of azinphos-methyl remained in these macrophytes on a mass basis. 41) The tail water contaminated with fluometuron, aldicarb and endosulfan from a cotton field was introduced to the non-vegetated open (Po) and vegetated (Pv, with several emergent macrophytes and water milfoil) ponds, and the concentration of each pesticide in water was monitored.…”