Lourens River Research Articles

Concentration, load and toxicity of spraydrift-borne azinphos-methyl at the inlet and outlet of a constructed wetland

Constructed wetlands have been widely used to treat different types of agricultural point and nonpoint source pollution including nutrients, sediments and some herbicides. However, very little is known about the effectiveness of constructed wetlands in controlling nonpoint source insecticide pollution. Here we describe the concentrations of total suspended solids (TSS), nutrients and spraydrift-borne azinphos-methyl (AZP) at the inlet and outlet of a 0.44-ha vegetated pond. One tributary, which receives contaminants from a 15-ha orchard area, flows directly through the wetland, before it enters the Lourens River, South Africa. A tracer experiment with Rhodamin B was undertaken to find the optimal timing for inlet and outlet sampling performance. The retentions of TSS, ortho-phosphate and nitrate during dry weather conditions were 15, 54 and 70%. Concentration levels of AZP were reduced below the wetland by 90.8±0.7%, from 0.65±0.08 to 0.06±0.01 μg/l ( n=5). The reduction of AZP load was 54.1±3.8%. A 24-h in situ bioassay employing midge larvae ( Chironomus spec.) revealed a significant (ANOVA, Fisher's PLSD; P≤0.01) reduction of toxicity. Mortality in two separate trials was 41.3±2.4% and 46.3±1.2% at the inlet station and 2.5±1.4 and 3.8±1.2% at the outlet station during days with spraydrift deposition into the tributary upstream of the wetland. During time intervals without any spraying in the catchment, mortality of the midge larvae in both trials was 1.2±1.2% at the inlet station and zero at the outlet station ( n=4 for each trial). We conclude that construction of small vegetated ponds is a suitable risk reduction strategy for agricultural nonpoint source insecticide input into surface waters.

Spray deposition of two insecticides into surface waters in a South African orchard area.

Drift from pesticide spray application can result in contamination of nontarget environments such as surface waters. Azinphos-methyl (AZI) and endosulfan (END) deposition in containers of water was studied in fruit orchards in the Western Cape, South Africa. Additionally, attention was given to the contamination in farm streams, as well as to the resulting contamination of the subsequent main channel (Lourens River) approx. 25 km downstream of the tributary stream inlets. Spray deposit decreased with increasing distance downwind and ranged from 4.7 mg m(-2) within the target area to 0.2 mg m(-2) at 15 m downwind (AZI). Measured in-stream concentrations of both pesticides compared well with theoretical values calculated from deposition data for the respective distances. Furthermore, they were in the range of values predicted by an exposure assessment based on 95th-percentile values for basic drift deposition (German Federal Biological Research Centre for Agriculture and Forestry [BBA] and USEPA). Pesticide deposition in the tributaries was followed by a measurable increase of contamination in the Lourens River. Mortality of midges (Chironomus spp.) exposed for 24 h to samples obtained from the AZI trials decreased with decreasing concentrations (estimated LC50 from field samples = 10 microg L(-1) AZI; lethal distance: LD50 = 13 m). Mortality in the tributary samples averaged 11% (0.5-1.7 microg L(-1) AZI), while no mortality was discernible in the Lourens River samples (0.041 microg L(-1)). The sublethal endpoint failure to form tubes from the glass beads provided was significantly increased at all sites in comparison with the control (analysis of variance [ANOVA], Fisher's protected least significant difference [PLSD], p < 0.01).

Rainfall-induced sediment and pesticide input from orchards into the lourens river, western cape, south africa: importance of a single event

Rainfall-induced runoff transported sediments and pesticides into the Lourens River and its tributaries during a 28.8-mm rainstorm in mid-December 1998. Average 1-h peak levels of current-use insecticides applied to adjacent orchard plots were 1.5μgl−1 azinphos-methyl, 0.2μgl−1 chlorpyrifos and 2.9μgl−1 total endosulfan (α, β, S) in the river itself. Respective average 1-h pesticide levels associated with suspended particles were 1247, 924 and 12082μgkg−1, along with 980μgkg−1 of prothiofos. Total suspended solids increased during runoff from 32 to 520mgl−1. The contaminated edge-of-field runoff entered the river via the tributaries directly bordering the orchard-growing areas. Increased concentrations of azinphos-methyl and prothiofos associated with suspended sediments were demonstrated to persist for about 3.5 months without any further input in one of the tributaries. This illustrates that the short-term exposure has the potential to result in long-term contamination of surface waters. In terms of chemical load during the 1-h peak discharge period, the single rainfall event caused a loss of 173gh−1 azinphos-methyl, 55gh−1 chlorpyrifos, 740gh−1 total endosulfan (α, β, S) and 41gh−1 prothiofos. Levels of contamination were extremely high; they exceed the national water quality standards and those established by the US EPA. A comparison with standard toxicity data and 24-h LC50s for the local amphipod species Paramelita nigroculus, obtained during this study, indicates that the concentrations found in the river may result in acute toxic effects on aquatic invertebrates and fishes. A probability analysis of 10-y rainfall data revealed that the frequency of a similar storm event occurring within the main spraying season is 1.7y−1.

Effectiveness of a constructed wetland for retention of nonpoint-source pesticide pollution in the Lourens River catchment, South Africa.

Constructed wetlands have been widely used to control both point- and nonpoint-source pollution in surface waters. However, our knowledge about their effectiveness in retaining agricultural 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 retention of runoff-related agricultural pollution. Total suspended solids, orthophosphate, and nitrate were retained in the wetland in the proportions 15, 54, and 70%, respectively, during dry weather conditions (with rainfall less than 2 mm/d) and 78, 75, and 84% during wet conditions (with rainfall between 2 and 35 mm/d). Retention of water-diluted azinphos-methyl introduced via runoff at a level of 0.85 microg/L was between 77 and 93%. Chlorpyrifos and endosulfan were measured during runoff in inlet water at 0.02 and 0.2 microg/L, respectively. However, both pesticides were undetectable in the outlet water samples. During a period of 5 months, an increased concentration of various insecticides was detected in the suspended particles at the wetland inlet: azinphos-methyl, 43 microg/kg; chlorpyrifos, 31 microg/kg; and prothiofos, 6 microg/kg. No organophosphorus pesticides were found in the outlet suspended-particle samples, highlighting the retention capability of the wetland. A toxicological evaluation employing a Chironomus bioassay in situ at the wetland inlet and outlet revealed an 89% reduction in toxicity below the wetland during runoff.

P269 Neuronal excitability alterations after facial nerve palsy

Spraydrift and edge-of-field runoff are important routes of pesticide entry into streams. Pesticide contamination originating from spraydrift usually resides in the water phase, while pesticides in contaminated runoff are to a large extent associated with suspended particles (SPs). The effects of two organophosphorous insecticides (OPs), chloropyrifos (CPF) and azinphos-methyl (AZP), on acetylcholinesterase (AChE) activity in rainbow trout were compared between two exposure scenarios, simulating spraydrift- and runoff-borne contamination events in the Lourens River (LR), Western Cape, South Africa. NOECs of brain AChE inhibition, determined after 1 h of exposure followed by 24 h of recovery, were 0.33 μg l−1 for aqueous CPF, 200 mg kg−1 for SP-associated CPF and 20 mg kg−1 for SP-associated AZP (at 0.5 g l−1 SP). The highest aqueous AZP concentration tested (3.3 μg l−1) was without significant effects. Previously reported peak levels of aqueous CPF in the LR (∼0.2 μg l−1) are close to its NOEC (this study), suggesting a significant toxicological risk to fish in the LR. By contrast, reported levels of SP-associated OPs in the LR are 20–200-fold lower than their NOECs (this study). In a comparative in situ study, trout were exposed for seven days at agricultural (LR2, LR3) and upstream reference (LR1) sites. No runoff occurred during the study. Brain AChE was significantly inhibited at LR3. However, OP levels at LR3 (CPF 0.01 μg l−1; AZP 0.14 μg l−1) were minor compared to concentrations having effects in the laboratory (see above). Additionally, muscle AChE activity was significantly higher in caged trout from LR1 than in animals maintained in laboratory tanks.