Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-04-17T23:51:07Z No. of bitstreams: 1 WanessaKalineDeAraujoMoura_TESE.pdf: 2835389 bytes, checksum: 2e690065461ca562c7c35cca77b810e5 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-04-21T00:20:21Z (GMT) No. of bitstreams: 1 WanessaKalineDeAraujoMoura_TESE.pdf: 2835389 bytes, checksum: 2e690065461ca562c7c35cca77b810e5 (MD5) / Made available in DSpace on 2017-04-21T00:20:21Z (GMT). No. of bitstreams: 1 WanessaKalineDeAraujoMoura_TESE.pdf: 2835389 bytes, checksum: 2e690065461ca562c7c35cca77b810e5 (MD5) Previous issue date: 2016-01-22 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / O trabalho de pesquisa objeto deste projeto foi desenvolvido na regi?o do baixo curso do rio Doce no munic?pio de Natal, nos bairros de Lagoa Azul, Paju?ara e Redinha, ao longo do Rio Doce, limite com o munic?pio de Extremoz, Rio Grande do Norte. A regi?o da plan?cie fluvial do Rio Doce localiza-se em Zona de Prote??o Ambiental (ZPA-9). Esta ZPA ? uma das que ainda n?o est?o regulamentadas e nela s?o observados diversos problemas ambientais decorrentes do uso e ocupa??o do solo, caracterizando um flagrante desrespeito ? legisla??o ambiental e cuja prote??o ? dificultada devido ? inexist?ncia de mecanismos legais espec?ficos. Este trabalho tem por objetivos implantar e estabelecer a manuten??o do cultivo da esp?cie Hyalella azteca (Crustacea, Amphipoda) no Laborat?rio de Ecotoxicologia - ECOTOX (UFRN) para avalia??o ecotoxicol?gica de sedimento; avaliar a qualidade da ?gua e do sedimento, utilizando os clad?ceros Ceriodaphnia dubia, Ceriodaphnia silvestrii e Hyalella azteca respectivamente, da regi?o do baixo curso do Rio Doce por meio de ensaios ecotoxicol?gicos e an?lises f?sicas e qu?micas de forma a avaliar a interfer?ncia das a??es humanas ao longo do rio. Foram realizadas visitas ? ?rea no per?odo de 2012 a 2014. Os locais de amostragem foram denominados LE, R2, R3, R4 e R5. A avalia??o da qualidade da ?gua e dos sedimentos do baixo curso do rio Doce, trecho localizado entre a Lagoa de Extremoz e a Redinha, por meio de an?lises f?sicas e qu?micas, e de ensaios ecotoxicol?gicos, na ?gua e no sedimento, nos anos de 2012, 2013 e 2014, embasou o conhecimento e respondeu as quest?es de pesquisa: nos testes ecotoxicol?gicos realizados em ?gua e sedimentos h? uma resposta mensur?vel da biota no ambiente aqu?tico, pois a altera??o encontrada nos par?metros f?sicos e qu?micos medidos em ?gua e os resultados negativos encontrados em pelo menos 50% dos testes de toxicidade cr?nica realizados mensalmente no per?odo de um ano evidenciaram o comprometimento da qualidade da ?gua do rio Doce pelo menos em parte do ano, destacando que as diversas atividades desenvolvidas no entorno da drenagem podem estar contribuindo para as varia??es observadas. / The object of this research project was developed on the lower course of the river Doce in the city of Natal, in the districts of Lagoa Azul, Paju?ara and Redinha, along the river Doce, limit with the municipality of Extremoz, Rio Grande do Norte. The region of the Doce river plain is located in the area of environmental protection (ZPA-9). This is one of the ZPA which are not yet regulated and are observed several environmental problems arising from the use and occupation of land, featuring a blatant disregard to environmental legislation and whose protection is hampered due to the lack of specific legal mechanisms. This work aims to deploy and establish the maintenance of cultivation of Hyalella azteca species (Crustacea, Amphipoda) in the laboratory of Ecotoxicology-ECOTOX (UFRN) for ecotoxicological assessment of sediment; assess the quality of the water and the sediment using the cladocerans Ceriodaphnia dubia, Ceriodaphnia silvestrii and Hyalella azteca respectively, the lower course of the Rio Doce for ecotoxicological tests and physical and chemical analyses in order to evaluate the interference of human actions along the river. The visits were carried out in the period from 2012 to 2014. Sampling sites were named LE, R2, R3, R4 and R5. The evaluation of the quality of the water and sediments of the lower course of the Doce river, excerpt located between the lagoon of Extremoz and Redinha, through physical and chemical analyses, and ecotoxicological tests, in water and sediment, in the years 2012, 2013 and 2014, served the knowledge and answered the questions of research: ecotoxicological tests carried out in water and sediments there is a measurable response of biota in aquatic environment because the change found in physical and chemical parameters measured in water and the negative results found in at least 50 of chronic toxicity tests conducted on a monthly basis within one year showed the commitment of the Doce river water quality at least part of the year, noting that the various activities carried out in the vicinity of drainage may be contributing to the observed variations.

Global climate change promotes warming temperatures and altered salinities that pose threats to aquatic ecosystems and species, such as Hyalella azteca. Moreover, these threats to aquatic ecosystems are exacerbated by agricultural, urban, and industrial pesticide runoff. In the state of California in 2012, pyrethroid insecticides were the seventh most applied group by licensed professional applicators for pest control and landscape maintenance. Some species, specifically H. azteca have developed non-target resistance to pyrethroids in California. It is imperative to understand whether the bioenergetic cost of resistance makes H. azteca more susceptible to warming and salinity effects in the presence of contaminants. This research presents an assessment on how multiple stressors can affect the toxicity of permethrin (pyrethroid insecticide) on one Wild-type and two pyrethroid- resistant species of H. azteca, belonging to different clades. A series of 96-h acute toxicity tests exposing animals to a concentration range of permethrin were performed with compounding stress from temperatures (18, 23 and 28 °C) and salinities (0.2, 1.0, and 6.0 practical salinity units [PSU]). Findings indicate resistant H. azteca cultured in pyrethroid-free settings have maintained resistance to permethrin over time, whereas the wild-type population did not develop any resistance over the course of experimentation. For resistant H. azteca, changes in salinity and temperature both increased and decreased survival of H. azteca exposed to permethrin. Between the two resistant clades, not only was survival affected, but the average slope of the dose-response curve was significantly different (p < 0.05); clade D was more susceptible to pyrethroids when coping with warming and higher salinity than clade C., Differential susceptibility potentially indicates that distinct resistance mutations confer a difference in the potency and mode of toxic action. The results provide insight to how changes posed by climate change, coupled with pyrethroid pesticides could be detrimental to this species, and conversely, how in some scenarios, changes to temperature and salinity might actually benefit the survival of H. azteca. These findings further indicate the importance of considering global climate change effects into risk assessments of emerging and legacy use contaminants.

Silver nanoparticles (AgNPs) are the most common nanomaterials incorporated in commercial products due to their antimicrobial activity. Recently, AgNPs were detected in surface waters suggesting the potential for bioavailability in the aquatic receptor organisms. This dissertation research attempts to understand the potential toxicity of AgNPs on water quality indicators, focusing on the microbial community and amphipods. This study evaluated whether: (1) the antimicrobial properties of AgNPs pose potential risks to microbial communities in pathogen impaired streams; (2) AgNPs can cause a shift in functional diversity and metabolic fingerprinting of microbial communities; (3) survival and growth of Hyalella azteca (amphipods) could be affected by AgNPs; and (4) surface coating agents influence AgNP toxicity in H. azteca. Microbial community responses to AgNPs were assessed using standard plate count, microbial enzyme assays, and carbon substrate utilization with Biolog EcoPlates™. Ten-day and 28-d toxicity tests were conducted in a static system to assess AgNP effects on H. azteca. AgNPs caused a 69% decrease in microbial concentration and a 77% decrease in β-glucosidase activity at 0.32 mg Ag kg-1 dry sediment. The substrate utilization pattern of the microbial community was altered by AgNPs at 0.33 mg Ag kg-1 dry sediment. Ten-day LC50s for the survival of H. azteca were 3.3, 9.2, and 230.0 µg Ag L-1 for AgNO3, citrate-AgNP, and PVP-AgNP, respectively, whereas the 28-d LC50s were 3.0, 3.5, and 66.0 µg Ag L-1 for AgNO3, citrate-AgNP, and PVP-AgNP, respectively. The EC20s for growth (calculated as biomass) for the 10-d test were 1.6, 4.7, and 188.1 µg Ag L-1 for AgNO3, citrate-AgNP, and PVP-AgNPs; while the 28-d EC20s for AgNO3, citrate-AgNP and PVP-AgNP were 3.2, 0.5, and < 50 µg Ag L-1. The NOECS for dry weight were 4 and 1, and 100 µg Ag L-1, while those for biomass were 2, 0.5, and < 50 µg Ag L-1 for AgNO3, citrate-AgNP, and PVP-AgNP, respectively. The overall toxicity followed the trend: AgNO3 > citrate-AgNP > PVP-AgNP. The studies suggest that AgNPs pose potential risks to microbial communities and epibenthic macroinvertebrates used as bioindicators of water quality to protect public health and ecosystem health.

Whether active or passive, dispersal accompanied by gene flow shapes the population genetics and evolutionary divergence of species. Indirect methods which use genetic markers have the ability to assess effective dispersal—that which resulted in gene flow. My objective was to see if an aquatic insect and an obligate aquatic invertebrate show similar phylogeographic patterns and genetic uniqueness. Hyalella azteca and Callibaetis americanus were collected from 4-5 springs in each of six basins in the Great Basin of western North America. No dispersal or genetic studies of C. americanus have been conducted to date. However, several studies focusing on mtDNA diversity of H. azteca have revealed a tremendous degree of cryptic diversity in the desert springs of the Great Basin. Nested clade phylogeographical analysis (NCPA), FST values, AMOVA, and Mantel tests were used to examine geographical associations. I also used traditional phylogenetic approaches including maximum parsimony (MP) and likelihood (ML) analyses using cytochrome c oxidase subunit I (COI), 28S, and 16S as genetic markers. The mitochondrial COI sequence divergences in C. americanus were higher than H. azteca COI divergences within springs but lower among springs. FST values were very high in H. azteca reaching near fixation for certain alleles. C. americanus FST values were lower suggesting greater gene flow and, consequently, greater dispersal rates. Even though Mantel tests did not detect significant isolation by distance when evaluating all haplotypes together, nested clade analysis was able to examine smaller networks of related haplotypes and detect significant isolation by distance. Whereas the genetic structure in C. americanus was dominated by restricted gene flow with isolation by distance, H. azteca was characterized more by gradual range expansion followed by fragmentation. Mayflies likely showed more gene flow than amphipods because of their flight capabilities, but movement was still restricted by long distances between isolated springs.

Hyalella azteca, an amphipod crustacean, is frequently used in freshwater toxicity tests. Since the mid-1980s, numerous organizations have collected and established cultures of H. azteca originating from localities across North America. However, H. azteca is actually a large cryptic species complex whose members satisfy both the biological and the phylogenetic species concepts. Recently, two publications reported that members of the H. azteca cryptic species complex have different toxicity responses to anions and an insecticide. In this study, four members of the H. azteca species complex were identified with DNA barcoding. The genetic variation among the four clades was consistent with interspecific distances between species. These lineages (clades 1, 3, 6, and 8) were cultured in identical conditions and monitored on a weekly basis to determine two life history traits: adult mortality and juvenile production. The large-bodied clades had significantly better survival and juvenile production compared to the small-bodied clade 3. Clade 6 had very low juvenile production and high mortality; therefore, was not included in this study. Unique culture protocols may be required for each clade to optimize growth, survival, and juvenile production in laboratory conditions. Genetic barcoding has identified only two clades in a survey of 17 laboratories. Therefore these two clades (1 and 8) were compared after exposure to copper and nickel 14-day toxicity tests. Clade 8 was 2.3-2.6 times more tolerant to copper exposure than clade 1 based on their LC50 and LC25. Similarly, clade 8 was more tolerant to nickel exposure than clade 1: LC50 was 1.8 times higher for the former. Nickel LBC50 and LBC25 were significantly different between clades by a factor of 2.1-2-8. Mortality (relative to copper concentrations in tissue), growth, and bioaccumulation responses were not significantly different based on overlapping confidence intervals. Although clades 1 and 8 are both large-bodied ecomorphs, these lineages had significantly different body mass (i.e., dry weight) after 14 days. The results of this study indicate that genetically characterized cultures of H. azteca should be used in toxicity tests.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2018-01-16T17:06:20Z No. of bitstreams: 1 ThiagoFariasNobrega_DISSERT.pdf: 1767927 bytes, checksum: 4bc39921c977a9668ed14d461e4bc936 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2018-01-19T14:01:37Z (GMT) No. of bitstreams: 1 ThiagoFariasNobrega_DISSERT.pdf: 1767927 bytes, checksum: 4bc39921c977a9668ed14d461e4bc936 (MD5) / Made available in DSpace on 2018-01-19T14:01:37Z (GMT). No. of bitstreams: 1 ThiagoFariasNobrega_DISSERT.pdf: 1767927 bytes, checksum: 4bc39921c977a9668ed14d461e4bc936 (MD5) Previous issue date: 2015-02-20 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Os efeitos delet?rios das atividades humanas ao meio ambiente s?o temas de v?rios estudos e consequentemente de mudan?as de paradigmas. Exemplo disso, ? que at? pouco tempo acreditava-se em um infinito poder de dilui??o dos ecossistemas em rela??o aos agentes t?xicos, e pouco se conhecia dos efeitos dos contaminantes aos organismos. Em ?reas de intenso crescimento urbano ? comum o descarte indiscriminado de subst?ncias t?xicas e consequentemente o desequil?brio das din?micas naturais dos ecossistemas. Dentre estes, os lagos s?o complexos e importantes fontes de ?gua superficial, abrigam esp?cies e t?m influ?ncia sobre o clima da regi?o ao seu redor. A Lagoa de Extremoz/RN, litoral Nordeste do Brasil, ? um corpo h?drico localizado numa regi?o de r?pido crescimento urbano. Est? sob influ?ncia de atividades rurais, urbanas e industriais, al?m do regime clim?tico prop?cio a per?odos prolongados de estiagem. O abastecimento de cerca de 300.000 pessoas depende da estabilidade h?drica dessa lagoa. O objetivo deste trabalho foi descrever as rela??es entre par?metros f?sicos, componentes qu?micos e as respostas observadas nos ensaios ecotoxicol?gicos, buscando informa??es sobre as varia??es sazonais. Para isso, foram realizadas, em dois anos, 2013 e 2014, an?lises f?sicas, qu?micas e ecotoxicol?gicas da ?gua e do sedimento superficial, em duas esta??es de amostragem na Lagoa de Extremoz (T1 e T2) e uma no rio Guajiru (T3). Nas amostras de ?gua foram aferidos o pH, turbidez, cloreto, OD, nitrato, nitrito, fosfato reativo total, metais e dureza. Para avaliar a toxicidade das amostras foram usados Ceriodaphnia dubia e C. silvestrii como organismos-teste. No sedimento foram aferidos os teores de carbonato, mat?ria org?nica e metais, caracteriza??o granulom?trica e avaliado os efeitos t?xicos sobre a sobreviv?ncia de Hyalella azteca. Verificou-se no per?odo de estiagem, ocorr?ncia de toxicidade aguda aos Hyalella azteca e nesse mesmo per?odo as concentra??es de metais em ?gua e sedimento tamb?m foram maiores. Em uma an?lise espacial percebeu-se que a maioria das amostras com efeito t?xico aos organismos-teste e com maiores concentra??es de metais foram coletadas na esta??o T2. Portanto, existem evid?ncias de que a qualidade da ?gua da Lagoa de Extremoz esteja diminuindo gradualmente e este processo se agrava pontualmente nos per?odos de menor pluviometria e na esta??o de amostragem T2. / The deleterious effects of human activities on the environment, are subject of several studies and therefore paradigm shifts. Until recently thought up in an infinite power dilution of ecosystems in relation to toxic agents, and little was known of the effects of contaminants to organisms. The intense urban growth contributes to the increase of toxic substances and the instability of the environment dynamics. Among these, the lakes are complex ecosystems important for sustaining life, by stock and provide water, to have influence on microclimates and others. The Extremoz Lake/RN, northeastern Brazil, is a water body located in a fast urban growth area. It is under the influence of rural, urban and industrial activities, further on the climate regime conducive to prolonged periods of drought. The supply of approximately 300.000 people depended on the hydraulic stability of this lake The aim of this study was to describe the relationship between physical, chemical components and the responses observed in the ecotoxicological tests, seeking information on seasonal variations. Physical, chemical and ecotoxicological analysis of water and surface sediment were held in two years, 2013 and 2014, in two sampling stations in Extremoz Lake (T1 and T2) and in Guajiru (T3) river. In all the water samples were measured pH, turbidity, chloride, DO, nitrate, nitrite, the total reactive phosphate, hardness and metals. Ceriodaphnia dubia and C. silvestrii as test organisms were used to evaluate the toxicity of the water samples. In the sediment were measured the carbonate, organic matter, metals, particle size, and evaluated the toxic effects on the survival of Hyalella Azteca. In dry season occurred acute toxicity to Hyalella azteca and in the same period the concentrations of metals in water and sediment were also higher. In a spatial analysis, it was noticed that most of the samples with toxic effects on test organisms and with the highest metal concentrations were collected at T2. So there is evidence that the Extremoz Lake quality is gradually declining and this process is occasionally worsens during periods of lower rainfall and sampling station T2.

No description available.

La calidad del agua de muchos ríos y arroyos se ve amenazada por las distintas actividades que el hombre realiza en las cuencas. Dada la importancia de la preservación y restauración de este valioso recurso, surge la necesidad de obtener nuevas herramientas que permitan evaluar de manera rápida, sencilla y fiable la calidad del agua, no limitándose sólo al análisis de sus características físico químicas, sino también a partir de las respuestas de la biota a las condiciones de su entorno. Por su ubicuidad, riqueza, sedentarismo y longevidad, los macroinvertebrados resultan apropiados como indicadores. En la presente investigación se evaluó la calidad del agua de arroyos pampeanos vinculados a distintos usos del suelo: urbano, industrial agrícola, ganadero y recreativo. En los arroyos Martín, El Pescado, Zapata y Buñirigo se estudió la calidad del agua desde diversas perspectivas, abarcando tanto aspectos bióticos como abióticos (variables fisicoquímicas del agua y características hidrológicas del cauce). Estos últimos incluyeron medidas tomadas en distintos niveles de organización, que van desde la bioquímica hasta los ensambles de macroinvertebrados, pasando por los individuos y haciendo énfasis en aspectos poblacionales de Hyalella curvispina (Crustacea: Amphipoda) y Pomacea canaliculata (Coenogastropoda: Ampulariidae). Los muestreos en esos arroyos se realizaron entre 2009 y 2010. En ellos se midieron parámetros fisicoquímicos y se analizó la calidad del hábitat físico (características del cauce y su vegetación) y de la biota (composición de los ensambles de macroinvertebrados, abundancias de especies sensibles y tolerantes e índices bióticos. A partir de los resultados de estas variables, se pudo establecer un orden decreciente de los arroyos en función de su calidad del agua: El Pescado > Zapata > Martín > Buñirigo. Simultáneamente, en esos arroyos se estudiaron rasgos poblacionales de P. canaliculata y H. curvispina como ser: densidad, biomasa, estructura etaria, proporción de sexos, fecundidad, fertilidad, crecimiento y supervivencia (los últimos tres sólo en P. canaliculata). Pese a que algunos de estos parámetros están influenciados por características del hábitat, la mayoría de los rasgos poblacionales analizados de ambas especies evidenciaron diferencias interpoblacionales que en general se correspondieron con los lo esperado según la calidad del agua. Alteraciones en el metabolismo de los individuos pueden repercutir en niveles de organización superiores alterando, por ejemplo, los valores normales de crecimiento y fecundidad. Dada la utilidad del estudio de la composición bioquímica para evaluar múltiples factores de estrés, tanto naturales como antropogénicos, se analizó el contenido de lípidos, proteínas y carbohidratos en huevos y tejidos (glándula de albumen y glándula digestiva) de hembras de P. canaliculata provenientes de los arroyos Martín, El Pescado, Zapata y Buñirigo. Las proporciones de lípidos, proteínas y carbohidratos en general fueron bajas en todos los tipos de muestras y evidencian poca relación con la calidad del agua, con una mayor variabilidad en la glándula digestiva. No obstante, las muestras del arroyo Martín presentaron valores más bajos que los de otros arroyos de estas sustancias, sugiriendo un peor estado nutricional. Esto concuerda con las menores tallas, tasas de crecimiento, fecundidad y fertilidad de los caracoles en este arroyo. Si bien estos resultados podrían ser consecuencia de la contaminación, no se descarta un posible efecto ligado al valor alimenticio de las macrófitas disponibles en ese arroyo. Con el fin de obtener otra herramienta de monitoreo, también se realizó una experiencia de exposición in situ con neonatos de P. canaliculata en los arroyos periurbanos El Gato, Rodríguez y Martín (los dos primeros muy contaminados) para evaluar la supervivencia frente a distintas calidades de agua. Estos caracoles mostraron ser sensibles a la contaminación, ya que en los arroyos más impactados se registró una mayor mortalidad que el sitio menos contaminado y en el control de laboratorio. Por lo tanto, se propone calibrar y validar esta herramienta en estudios de calidad del agua y monitoreo de arroyos pampeanos. El enfoque de esta investigación, abordada a través de múltiples niveles de organización, permitió obtener mayor información acerca del estado de los cuerpos de agua estudiados y discriminar los rasgos poblacionales que podrían constituir buenas herramientas para la evaluación de la calidad del agua por ser más sensibles. Asimismo, se destaca la necesidad de evaluar la calidad de los ecosistemas con un enfoque holístico, contemplando la interacción de los macroinvertebrados con las variables ambientales que operan en la regulación de sus poblaciones.

Silver nanoparticles (AgNPs) are known to cause ecotoxic effects, but there are no existing derived ambient water quality criteria (AWQC) for these nanomaterials to protect freshwater aquatic life due to insufficient toxicological data. We exposed Hyalella azteca to silver nitrate, citrate-coated AgNPs (citrate-AgNPs), and polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs) in a 10-day and 28-day water-only static renewal system with clean sand as a substrate for the amphipods and compared their point estimates with the United States Environmental Protection Agency (USEPA) AWQC for silver. We observed that all treatments decreased the survival, growth, and biomass of H. azteca, and the order of toxicity was AgNO > citrate-AgNPs > PVP-AgNPs. The LC50s of AgNO, citrate-AgNPs, and PVP-AgNPs were 3.0, 9.6, and 296.0 µg total Ag L, respectively, for the acute exposure and 2.4, 3.2, and 61.4 µg total Ag L, respectively, for the chronic exposure. Acute and chronic EC20s of citrate-AgNPs ranged from 0.5 to 3.5 µg total Ag L while that of PVP-AgNPs ranged from 31.2 to 175 µg total Ag L for growth and biomass. Both Ag released from AgNPs and the nanoparticles contributed to the observed toxicity. The dissolution and toxicity of AgNPs were influenced by surface coating agents, particle size, and surface charge. Most point estimates for AgNPs were above AWQC for silver (4.1 µg L) and the lowest concentration (0.12 µg/L) at which Ag is expected to cause chronic adverse effects to freshwater aquatic life. Our study demonstrates that the current AWQC for silver, in general, is protective of freshwater aquatic life against AgNPs tested in the present study.

A literature review of metal mixture interaction analyses identified that there was not a consistent method to determine the impact of metal mixtures on an aquatic organism. The review also revealed that a majority of the research on mixtures made use of water concentrations only. Therefore research was conducted to determine the relationship between exposure, bioaccumulation and chronic effects of the four elements As, Co, Cr and Mn individually. Mechanistically based saturation models of bioaccumulation and toxicity were determined for the benthic invertebrate Hyalella azteca, from which lethal water concentrations and body concentrations were also determined. These models were then combined with those previously done for the metals Cd, Cu, Ni, Pb, Tl and Zn to model the impact of 10 metal mixtures on bioaccumulation in short term (1-week) exposures and on bioaccumulation and toxicity in chronic (4-week) exposures at “equi-toxic” concentrations. Interactions between the metals were identified in which; Cd, Co and Ni bioaccumulations were significantly inhibited, Tl and Zn bioaccumulations were marginally inhibited, there was no impact on Cr, Cu or Mn bioaccumulation, and both As and Pb bioaccumulation were enhanced by some mixtures of metals. It was determined that strict competitive inhibition may be a plausible mechanism of interaction affecting Co, Cd and Ni bioaccumulation but not for any of the other metals. However, it is possible that other interactions such as non-competitive or anti-competitive inhibition may have been responsible. A metal effects addition model (MEAM) was developed for Hyalella azteca based on both the bioaccumulation (body concentrations) to effects and the exposure (water concentration) to effects relationships developed from the single metal only studies The MEAM was used to predict the impact of metal mixture exposures on mortality. Toxicity was under-estimated when based on measured water or body concentrations, however, its best prediction was based on body concentrations. The MEAM, when based on measured body concentrations, takes bioavailability into account, which is important since the chemical characteristics of water can greatly alter the bioavailability and therefore toxicity of metals. The MEAM was compared to the traditional Concentration Addition Model (CAM), which calculates toxic units based on water concentrations and LC50s or body concentrations and LBC50s. The CAM overestimated toxicity, but had its best prediction when based on water concentrations. Over all, the best fit to observed mortality was the prediction by the MEAM, based on body concentrations. The measurement of bioaccumulated metals and the use of the MEAM could be important in field site assessments since it takes into account changes in bioavailability due to different site water chemistries whereas the traditional CAM based on water concentration does not.