Conserving aquatic resources is an important consideration in the development of environmentally sound agricultural practices. Over 1.1 million kilograms, or 2,425,500 pounds, of the insecticide terbufos are used on about 18 percent of Iowa\u27s corn-producing acres annually, creating significant potential for contamination of surface waters. Even when properly applied, such pesticides often enter nearby streams where they can potentially affect the organisms present. Although many such agrichemical contaminants find their way to Iowa\u27s streams and rivers, little research has been conducted to determine their effects on stream organisms

Pontasch, Kurt W.

English

Name not available

Multispecies toxicity tests using indigenous organisms: predicting pesticide effects in streams

Conserving aquatic resources is an important consideration in the development of environmentally sound agricultural practices. Over 1.1 million kilograms, or 2,425,500 pounds, of the insecticide terbufos are used on about 18 percent of Iowa's corn-producing acres annually, creating significant potential for contamination of surface waters. Even when properly applied, such pesticides often enter nearby streams where they can potentially affect the organisms present. Although many such agrichemical contaminants find their way to Iowa's streams and rivers, little research has been conducted to determine their effects on stream organisms.</p

Pontasch, Kurt

Digital Repository @ Iowa State University (ISU)

90-37 COMPETITIVE GRANTLeopold Center LEOPOLD CENTER FOR SUSTAINABLE AGRICULTURE Multispecies toxicity tests using indigenous organisms: predicting pesticide effects in streams REPORT Principal investigator Kurt W. Pontasch Biology University of Northern Iowa Cedar Falls Budget $20,000 for year one $24,090 for year two Background and goals Conserving aquatic resources is an important consideration in the development of environ­mentally sound agricultural practices. Over 1.1 million kilograms, or 2,425,500 pounds, of the insecticide terbufos are used on about 18 percent of Iowa's corn-producing acres annually, creating significant potential for con­tamination of surface waters. Even when properly applied, such pesticides often enter nearby streams where they can potentially affect the organisms present. Although many such agrichemical contaminants find their way to Iowa's streams and rivers, little research has been conducted to determine their effects on stream organisms. Managing these hazards to aquatic ecosys­tems requires predictive techniques that are both cost-effective and accurate. Studies by the U.S. Environmental Protection Agency have demonstrated correlations between re­sponse of single species to these chemicals in laboratory tests and field tests. However, such tests cannot predict how much and what kind of damage may occur to the overall ecosys­tem. The multispecies toxicity tests under­taken in this project were designed to avoid the cost of underprotection—namely, damage to natural resources—as well as avoid the cost of overprotecting the environment by establishing regulatory requirements that pro­vide no biological benefit Multispecies toxicity tests examine a broad range of species that naturally coexist and consider interactions between species. More­over, they are conducted under environmen­tally realistic conditions. Although research­ers have used ponds to predict pesticide ef­fects on natural communities, they know little about the sensitivity of stream communities to these inputs, even though streams are exposed more frequently than lakes and ponds to non-point source agricultural pollutants. The objectives of this project were to develop and test a multispecies toxicity testing system capable of predicting the effects of two major corn insecticides, fenvalerate and terbufos, on stream insect communities. Primary emphasis was placed on aquatic insects because (1) they constitute the majority of macroinvertebrate species and individuals in most streams and rivers, and (2) they exhibit a wide range of tolerances to stressors because of their mor­phological, physiological, and ecological di­versity. Insects in this study included may­flies, stoneflies, caddisflies, riffle beetles, and midges. Approach and methods The study was conducted in the Ecosystem Simulation Laboratory at the University of Northern Iowa (UNI). This laboratory is the only one in Iowa, and one of only a few in the country, with capabilities for testing contami­nant effects on stream communities. The facility consists of 15 oval, artificial streams, or microcosms, constructed of molded fiber­glass (see Fig. 1). Investigators tested two corn insecticides com­monly used in Iowa: fenvalerate, the active ingredient in Pydrin®, and terbufos, the active ingredient in Counter®. Fenvalerate has be­come popular because of its very low toxicity to humans, and terbufos is the most widely used corn rootworm insecticide in Iowa. In recent years, synthetic pyrethroid insecticides like fenvalerate have taken an increasing share Leopold Center Progress Reports 13 Fig. 1. Artificial stream mesocosms in the lab. Each stream channel measures 1.7by 0.24 by 0.13 meters. of the pesticide market because they also con­trol insects effectively while showing low tox­icity in birds and mammals. These pyre­throids' popularity and environmental stabil­ity increase the possibility of unintentional exposures in aquatic ecosystems where non­target organisms may be adversely affected. Twelve to thirteen million acres of corn are planted in Iowa each year and approximately six million of these acres are treated for corn rootworm. Terbufos, an organophosphorus insecticide, is widely used in agriculture to control surface and soil feeding insects be­cause it is highly toxic to a variety of target organisms, has low water solubility, and is persistent in a variety of soil types. Previous studies indicate its potential for adversely af­fecting non-target organisms. Yet, most stud­ies of its effects on non-target insects have used terrestrial rather than aquatic organisms. Initially, the investigators colonized a food source (periphyton) on foam units in a riffle area along the Volga River in northeastern Iowa. They then transported these units to the laboratory streams in an aerated cooler, where the periphyton developed for five weeks prior to beginning the toxicity tests. The insects were colonized in the Volga River riffle area in 64 rock-filled plastic containers having six circular holes in each side. The artificial substrates were secured to wooden frames that had been anchored to the stream bottom with iron rods and concrete blocks. After several weeks, the artificial substrates were transferred to coolers filled with river water and transported to the laboratory, where they were randomly assigned to the 15 artifi­cial streams. The macroinvertebrates were allowed to acclimate for two days before dos­ing began. The investigators used five stock solutions of 0.0, 1.0, 10.0, 100.0, and 1000.0 |0g/L (parts per billion) active ingredient for both fenvalerate and terbufos. These solutions were replaced every three days, which was espe­cially important for terbufos because of its short half life (the time it takes for half the active ingredient to disappear). The stock solutions were mixed with dilution water to establish concentrations of 0.0, 0.01, 0.1, 1.0, and 10 |ig/L in the artificial streams; each concentration was tested in triplicate. Com­plete replacement of water occurred approxi­mately every three hours. Each stream was covered by an emergence net; overhead lights placed over each stream simulated a period of daylight corresponding to that on day 15 of the test. Stream volume and the circular current in each microcosm were maintained mechani­cally. During the test period, investigators sampled water from each microcosm on days 10, 20, and 30 to determine actual insecticide concen­trations. In addition, they monitored dissolved oxygen, pH, conductivity, alkalinity, water hardness, temperature, and current velocity to ensure that the stream microcosms reflected those parameters in the natural source ecosys­tem. Investigators quantified dead and dying macroinvertebrates (referred to as "drift") by placing a dip net for one minute in the stream one hour after the initial dose. The insects entering the drift were identified, counted, and returned to the microcosm. Emergent adult insects were sampled and preserved every 48 to 72 hours. After 30 days, the contents of each microcosm were washed through a sieve, after which insects were sorted by hand and classi­fied according to size. With the exception of Volume 2 (1993) 14 midges (Chironomidae: Diptera), insects were identified to the lowest possible taxonomic unit using appropriate references, and the spe­cies abundances of both adults and immatures were determined for each microcosm. In determining the abundances of various spe­cies, macroinvertebrate taxa that had mean densities greater than or equal to four in at least one treatment were considered a "core" taxon. Total insect densities for each core taxon were compared over all experimental groups to de­termine concentration effects. Data were ana­lyzed by established statistical procedures. Findings Fenvalerate: Because most field exposures are episodic events, the continuous exposures during these 30-day tests subjected riffle in­sect communities to worst-case conditions. However, drift responses to the initial dose (see Fig. 2) do suggest that short-term expo­sure to 1.0 |ig/L fenvalerate will result in significant impact on riffle insect community structure. (Conversely, it does not appear that short-term exposure to the terbufos concentra­tions tested severely impacts riffle insects; see terbufos findings below). The insects most frequently entering the drift were mayflies and caddisflies. Under field conditions, fenvalerate may enter aquatic ecosystems through agri­cultural runoff, aerial drift, or accidental spills. The initial fenvalerate dose in this study, which simulated short-term exposures in the field, indicated that concentrations above 1.0 [XgfL will significantly increase drift from the im­pacted areas. Analysis of all taxa found during the 30-day test revealed a significant reduction in species richness and total density at 0.1 \ig/L fenvalerate. Density reductions were signifi­cant in the 0.01 |ug/L treatment for one species each of stonefly and larval caddisfly. This finding precluded determination of a commu-nity-level NOEC (no observable effect con­centration, an individual, standardized con­centration limit applied by the U.S. EPA to widely used pesticides). As nominal concen­trations increased from 0.01 to 0.1 jiig/L fenvalerate, eight core taxa experienced sig­nificant density reductions, and the same stonefly species was completely eliminated. With the exception of two caddisfly pupae and a few solitary other larvae remaining in the 10.0 |Ug/L microcosms, riffle insect communi­ties were completely eliminated as nominal concentrations increased from 1.0 to 10.0 jog/ L fenvalerate. In short, this study indicates that aqueous fenvalerate concentrations be­tween 0.01 and 0.1 |ig/L will interrupt normal biotic processes in streams and rivers by im­pacting riffle insect community structure and function. Terbufos: Initial terbufos exposures did not result in significant drift response in any of the concentrations tested. After the 30 days, four taxa, including the most abundant caddisfly, another caddisfly, and two types of midges, exhibited significant mortality at 10 |ig/L rela­tive to controls. Species richness and total density were also significantly reduced at 10 \xgfL terbufos. However, densities of all taxa in the 1.0 Hg/L treatment were similar to those in the control streams. Overall, the data suggest the following with respect to riffle insect communities: that sig­nificant impact occurs at concentrations near 10 |ig/L, the NOEC lies above 1.0 |ug/L, and terbufos is not as toxic as fenvalerate. There-Fig. 2. Mean number of immature aquatic insects from one-minute drift samples taken one hour after the initial fenvalerate pulse dose. Treatments with the same letter are not significantly different. Leopold Center Progress Reports 15 For more information contact K. W. Pontasch, University of Northern Iowa, Cedar Falls, Iowa, 50614, (319)273-2098. fore, if terbufos inputs are regulated to prevent concentrations from exceeding 1.0 |ig/L, it should be possible to avoid deleterious effects on riffle insect communities. Implications Pesticides will continue to play a role in sus­tainable agriculture in Iowa and elsewhere. Still, in our efforts to reduce pesticide inputs, it is important to know how much and what kinds of deleterious effects a given pesticide concentration will cause in various ecosys­tems. By developing NOECs for widely used pesticides, we can set goals for reducing their input so that the NOEC for a given ecosystem is not exceeded. For example, this research suggests that NOECs for communities of insects commonly found in Iowa streams lie below 0.01 (ig/L fenvalerate and above 1.0 (ig/L terbufos. Armed with this information, we should attempt to insure that these NOECs are never reached in Iowa's streams. Although data are unavailable on fenvalerate and terbufos concentrations in Iowa streams, the suggested application concentrations are several times higher than the concentrations used in these studies. Thus these concentra­tions are probably environmentally realistic for situations where fenvalerate and terbufos reach stream ecosystems. Further research is needed to monitor actual concentrations of these and other pesticides in Iowa surface waters. This research has provided a large body of information on pesticide effects on non-target insects living in streams and rivers. These stream insect communities are the most likely aquatic organisms to suffer pesticide expo­sure, but information on how pesticides affect them has rarely been collected. However, toxicity data from the U.S. Fish and Wildlife Service indicate that Pydrin® is more toxic to fish than Counter®; thus, these insecticides appear to have the same impact in aquatic organisms higher in the food chain. Further research into the effects of widely used pesti­cides on stream communities should be con­ducted in order to establish scientifically justi­fiable NOECs that will protect our aquatic resources. The results of this project have been presented to a number of local civic and environmental organizations. The Izaac Walton League's national Save our Streams project has also shown strong interest in the data resulting from this project. Volume 2 (1993) 16 

https://dr.lib.iastate.edu/bitstreams/0341867f-d666-4237-9efe-560f3f6b7e15/download

Multispecies toxicity tests using indigenous organisms: predicting pesticide effects in streams

Abstract

Similar works

Full text

Available Versions

Name not available

Digital Repository @ Iowa State University (ISU)