Sublethal Effects Of Toxic Chemicals On Aquatic Animals

Author : Krista Callinan Hoffmann
Publisher :
ISBN 13 : 9781321806335
Total Pages : pages
Book Rating : 4.8/5 (63 download)

DOWNLOAD NOW!

Download or read book The Toxicant Mixing Pot written by Krista Callinan Hoffmann and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thousands of chemicals are discharged into natural water bodies each day, yet there are vast information gaps on the toxicity of multiple common contaminants in mixtures and their effects on aquatic species. Contaminant mixtures can interact (synergistically or antagonistically) or they can be additive. Most contaminant mixtures are additive, however the toxic mechanisms of the component chemicals in a mixture can determine how the toxic responses add up. Where chemicals have the same or similar mechanisms of action, mixtures are expected to add up as if the chemicals were dilutions of one another. This response is described as the model of Concentration Addition (CA). Chemicals with different mechanisms of action, on the other hand, will theoretically still be more toxic in combination than alone, and the resulting effects will be based on the summed probability of response to either of the chemicals individually. This response is described as the model of Independent Action (IA). As three separate research projects, this dissertation tests the toxic effects and interactions of multiple common aquatic contaminant mixtures using statistical regression analyses coupled with model comparisons, to investigate whether known mechanisms of toxic action explain mixture effects on lethal and sublethal endpoints. The first two chapters test a variety of pesticides and contaminants that are environmentally prevalent and toxic, while the third chapter investigates the lethal and sublethal effects of herbicides and adjuvants for which the toxicities were previously unknown. Urban, agricultural and industrial areas commonly occur immediately alongside some of the most biodiverse and sensitive aquatic environments world-wide. In the San Francisco Bay-Delta (California, USA), contaminants have been a pervasive problem the late 19th century. Chemicals selected for this research were based on current water quality monitoring results from the SF Bay-Delta region (California, USA), but all of the compounds have been found at toxic levels in surface water across the U.S. and other nations. Pyrethroid insecticides are applied to urban and agricultural landscapes and use has progressively increased over the past 20 years. Many pyrethroids are commonly detected at toxic concentrations in the surface water and sediment of water bodies world-wide. Multiple field studies implicate pyrethroid mixtures in environmental toxicity and ecological degradation. In chapter one, I examined the interactions of all possible mixtures of two Type I and two Type II pyrethroid pesticides on mortality, swimming motility and growth in the epibenthic amphipod, Hyalella azteca, a common prey species to native fish in the Delta and other water bodies across the U.S. Though the effects of pyrethroid mixtures should theoretically be additive by CA, previous studies have resulted in variable responses. This study used a novel two tiered analytical approach including regression analysis and model comparisons to specifically characterize interactions of multiple pyrethroid pesticides on lethal and sublethal endpoints. As such, this study was the most comprehensive analysis of pyrethroid mixture toxicity to date. Pyrethroids were toxic to the amphipod, H. azteca, at environmentally relevant concentrations and most mixtures were concentration additive, following the model of CA. The only exception was the acute 4d exposures of cyfluthrin, a Type II pyrethroid, with either of the two Type I pyrethroids, bifenthrin and permethrin. Mechanistically, target site-specific competition could explain the interactions and additive responses of pyrethroid mixtures found in the current and previous studies. All mixtures were concentration additive on the sublethal endpoints of swimming motility and growth. In chapter one, mixtures of pyrethroids were additive by either CA or IA upon all endpoints tested, however interactions of pyrethroids with other anthropogenic chemicals that are prevalent in the environment were still uncertain. In chapter two, I investigated the effects of the pyrethroid, bifenthrin, in mixtures with copper, ammonia and the organophosphate pesticide, chlorpyrifos. Different mechanisms of toxicity theoretically result in additive interactions by the model of IA, and this study sought to verify this hypothesis. Hyalella azteca was again used as the model organism, with mortality, swimming motility and growth as the endpoints tested. Additive responses varied depending on the chemicals tested and exposure duration. Both bifenthrin x chlorpyrifos and bifenthrin x copper were additive by the model of IA after the 4d exposure, but were additive by CA after 10d. Bifenthrin and ammonia, on the other hand were less than additive by either model after both 4d and 10d exposures. Results indicate that even chemicals targeting different biological sites in an organism can be concentration additive, therefore additive response may be generalizable to a target pathway, such as neurotoxicity. Further, divergent mixture responses across time points imply that there may be different mechanisms of toxicity over acute versus chronic exposures. Acute responses may be more specific to a target organ or tissue site, where as chronic exposures may result in greater levels of general effects, such as metabolic stress and cellular necrosis. Bifenthrin and ammonia were less toxic than predicted by either additive model, most likely a product of their opposing effects on Na+/K+ ATPase transporters. While chapters one and two dealt with common mixtures of contaminants discharged from urban, industrial and agricultural sources, chapter three addresses the toxic effects of herbicides and herbicide-adjuvant mixtures that are directly applied into waterways for the control of invasive aquatic vegetation. Because of their wide-spread and direct use within waterways, environmental concentrations of these herbicides can be substantial following herbicide applications, therefore characterizing the effects on sensitive species like delta smelt is critical. Two herbicides, imazamox and penoxsulam, and their adjuvant, Agridex, were tested over 96h exposures using hatchery reared delta smelt embryo and larvae. The toxic mechanism of action of the two herbicides tested is specific to amino acids found in the cell walls of plants that do not occur in animals, therefore any effects in animal species would be due to different mechanisms. As such, multiple lethal and sublethal endpoints were analyzed to investigate the stress response in delta smelt to these chemicals, including embryo hatching success, larvae survival, hatchling/larvae condition (as condition factor) and energy stores (as yolk sac oil globule area). Smelt survival and hatching success were not sensitive to the chemicals or mixtures tested, except at the highest treatment concentrations, hundreds of times greater than expected in the environment. Sublethal responses of condition factor and oil globule area were negatively affected, however, at low environmentally relevant concentrations of the adjuvant, Agridex. Where effects on hatching success and larvae survival were significant, herbicides and Agridex interacted antagonistically, while significant sublethal effects on embryo oil globule area and condition factor were largely additive.