阿特拉津对BALB／c小鼠T淋巴细胞功能的影响

目的探讨阿特拉津对小鼠T淋巴细胞功能的影响。方法健康BALB／c小鼠按体重随机分为阿特拉津高剂量组（400mg／kg）、中剂量组（200mg／kg）、低剂量组（100mg／kg）和阴性对照组（蒸馏水）,经口灌胃,每天1次,连续21d。试验结束后,眼球取血,处死小鼠,观察胸腺组织病理学变化,采用MTY还原法和流式细胞仪分别检测脾脏T淋巴细胞增殖情况和胸腺T淋巴细胞亚群分布,酶联免疫吸附法检测血清中白细胞介素-2（interleu—kin-2,IL-2）和白细胞介素．4（interleukin-4,IL-4）含量。结果阿特拉津暴露使小鼠胸腺皮质细胞减少,各剂量组脾脏T淋巴细胞转化率低于阴性对照组（均有P〈0．05）。阿特拉津中、高剂量组胸腺CD3＋T淋巴细胞亚群比例以及CD4＋T／CD8＋T比值均低于阴性对照组（均有P〈0．05）,各剂量组CD4＋T淋巴细胞亚群比例均明显低于阴性对照组（均有P〈0．05）,CD8＋T淋巴亚群比例随染毒剂量增高有降低趋势,但差异无统计学意义（均有P〉0．05）。阿特拉津高剂量组血清IL-2和IL4含量明显降低（均有P〈0．05）。结论阿特拉津能抑制小鼠T淋巴细胞功能,因而有免疫毒性作用。     

大豆异黄酮对雄性子代大鼠P450scc、MRβ基因表达的影响

[目的]探讨孕期大鼠暴露大豆异黄酮对子代雄性生殖系统发育的影响。[方法]SD大鼠按雌：雄=2：1的比例同笼交配获取40只孕鼠。将孕鼠随机分为5组：对照组（0mg／kg）;大豆异黄酮25、50、150、450mg／kg组。在孕期第13-19天将大豆异黄酮以花生油为溶剂灌胃染毒。将雄性子代于出生后第18天处死取其睾丸组织用荧光定量PCR（Real-time PCR）检测胆固醇侧链裂解酶（P450scc）、苗勒管抑制物（M／S）和13一雌激素受体（E即）基因的表达水平。[结果]大豆异黄酮可以明显降低E即基因的表达（P〈0．05）;P450scc基因表达的降低不明显;在150mg／kg和450mg／kg剂量时可以增加M／S基因的表达（P〈0．01）。[结论]孕期暴露大豆异黄酮后可以改变雄性子鼠睾丸的基因表达水平,从而对子鼠的雄性生殖系统发育造成影响。     

大豆异黄酮对动脉硬化大鼠的抗氧化作用研究

目的研究高含量大豆异黄酮（soy isoflavones,SI）对高脂型动脉粥样硬化大鼠动脉斑块面积及体内氧化酶活力、过氧化脂质的影响。方法国内首次采用总异黄酮含量为72．35％（金雀异黄素含量28．49％）的大豆异黄酮作为受试物，设30mg／kg体重、90mg／M体重、270mg／M体重3个剂量组，同时设雌激素（已烯雌酚）对照组，与动脉粥样硬化（atheroselelmis,AS）高脂模型组、正常饲料对照组，喂饲Wistar大鼠，经一段时间，检测血液、肝脏抗氧化酶如超氧化物歧化酶（SOD）、谷胱甘肽过氧物酶（GSH—Px）及总抗氧化活力（T—AOC）和过氧化脂质产物丙二醛（MDA）的浓度并用计算机图像分析粥样斑块面积。结果添加高含量大豆异黄酮的饲料组大鼠血液和肝脏中SOD、GSH—Px、T—AOC等抗氧化酶的活力升高，过氧化脂质产物MDA的含量降低，动脉粥样斑块形成面积显著减少（P〈0．05），且有明显的剂量-效应关系。结论大豆异黄酮在高脂型动脉粥样硬化大鼠体内发挥抗氧化作用，抵抗动脉粥样硬化的形成。     

丁草胺对斑马鱼及其胚胎发育毒性影Ⅱ向的研究

目的探讨丁草胺对斑马鱼及其胚胎的发育毒性,并确定其最大未观察到有害作用浓度。方法参照OECD推荐的方法,选用急性毒性试验、肝脏酶活性测定及胚胎发育毒性试验进行研究。斑马鱼及其胚胎通过水环境暴露接触丁草胺后,分别测定LC50、超氧化物歧化酶（SOD）活性、腺苷三磷酸酶（ATPase）活性、孵化率、死亡率、畸变率等指标。结果 丁草胺对斑马鱼的96h LC50为0．951mg／L（95％可信限：0．681～1．313mg／L）,属极高毒类除草剂。在0．16～0．32mg／L浓度范围内,丁草胺对SOD酶活性有抑制作用;在0．08～0．32mg／L浓度范围内,丁革胺对Aq、Pase酶活性有抑制作用。丁草胺对斑马鱼胚胎的发育也有明显的影响。对照组与丁草胺各处理组的120h孵化率分别为96％、92％、72％和44％,120h死亡率分别为2％、4％、10％和20％,120h畸变率分别为2％、2％、10％和16％。丁草胺处理组的孵化牢低于对照组,死亡率、畸变牢高于对照组。与对照组相比,0．018和0．036mg／L丁草胺处理组胚胎发育明显迟缓,仔鱼身长明显变短,差异有统计学意义。结论丁草胺是一种高毒除草剂,对斑马鱼肝脏ATPase和SOD酶活性有抑制作用,能致斑马鱼胚胎发育迟缓和畸变。在本试验条件下,丁草胺最大未观察到有害作用浓度为0．009mg／L。     

铀尾矿浸出液成分分析及其对斑马鱼的氧化应激损伤

[目的]观察铀尾矿浸出液对斑马鱼[zebrafish（Daniorerio）]的毒性影响,为评价铀尾矿对机体的危害性及潜在环境风险提供科学依据。[方法]采用火焰原子吸收法测定铀尾矿浸出液中重金属的含量,TRPO-环已烷／2-（5-溴代-2-啶基偶氮）-5-间苯二酚分光光度法测定铀含量,其他成分的分析参照国际标准进行;标准稀释水将铀尾矿浸出液稀释为0．05％、0．25％、0．5％及1％4个浓度组染毒斑马鱼,暴露7d后,测定斑马鱼肌肉、鳃和肝脏三种组织中超氧化物歧化酶（SOD）,过氧化氢酶（CAT）,钠、钾离子三磷酸腺苷酶（Na’-K’-ATP酶）活性和丙二醛（MDA）含量的变化情况。[结果]铀尾矿浸出液中的铀含量为0．0628mg／L,超过WHO规定的饮用水中铀浓度限值约4倍。斑马鱼在设计染毒液中暴露7d后,三种组织中SOD活性显著降低（P〈0．05）,而肌肉及肝脏的SOD活性在低浓度组出现升高（P〈0．05）,SOD活性可能存在暴露时间与浓度效应关系。鳃CAT活性在暴露7d后出现了下降（P〈0．05）,且随暴露浓度的升高而降低,最高抑制率为84．8％,表明腮内出现了早期的氧化应激反应。三种组织中,随着铀尾矿浸出液染毒浓度增大,Na’-K＋-ATP酶活性下降（尸〈0．05）,而MDA含量呈上升趋势。[结论]铀尾矿浸出液对机体危害可能主要是铀的毒性所致。降低氧化应激损伤水平可能是预防和保护机体免受铀尾矿浸出液毒害的有效靶点之一。     

杀虫安的最大无作用剂量

目的研究杀虫安对大鼠的亚慢性毒性，求出最大无作用剂量。方法按照GB15670—1995《农药登记毒理学试验方法》中亚慢性90天毒性方法，雌雄性大鼠均设低（7．5mg／kg）、中（30mg／kg）、高（120mg／kg）3个剂量组和1个对照组，测试指标包括血液学、尿液、血液生化检查，病理学检查，每周1次测定体重、进食量，到期解剖，测定脏器重量，对结果进行统计学处理。结果杀虫安中剂量组ALP低于对照组，肝、肾脏重量、肝／体、肾／体比高于对照组；高剂量组ALP低于对照组，心脏重量高于对照组，雌性大鼠心／体比、肾／体比、 肝／体比高于对照组，雄性大鼠脑、肝、脾、肾、心脏重量、脾／体、肝／体比高于对照组。组织病理学检查显示中、高剂量组肝、肺的病变率较高。结论杀虫安原药最大无作用剂量雌性为（0．62±0．03）m/（kg．d），雄性为（0．56±0．03）m/（kg．d）。     

大豆异黄酮对肥胖大鼠血脂及瘦素水平的影响

目的：通过大豆异黄酮（SIF）对肥胖大鼠的干预，观察大鼠体重、血脂及血清瘦素水平的变化，探讨SIF对肥胖大鼠的减肥作用及机制。方法：用高脂饲料造成雄性大鼠肥胖模型，然后按体重将其随机分为4组，各组均继续给予高脂饲料。其中一组为肥胖对照组，灌胃生理盐水，另外三组灌胃SIF，剂量分别为50mg／kg BW、150mg／kg BW及450mg／kg BW。第4周末股动脉取血，用酶免法检测血浆中瘦素，酶法检测血脂。结果：与肥胖对照组相比，450mg／kg BW剂量组大鼠血清瘦素水平明显升高，大鼠体重、血清TG、TC水平降低（P〈0．05或P〈0．01）；150mg／kg BW剂量组大鼠的体重及血清TC水平降低（P〈0．05）。结论：SIF对肥胖大鼠有减肥作用，机制可能与SIF调节瘦素表达和分泌有关。     

Aroclor1254对斑马鱼胚胎发育、肝脏组织结构及其卵黄蛋白原基因的影响

[目的]使用脊椎动物模型斑马鱼评价Aroclor1254对斑马鱼胚胎发育、肝脏组织结构以及卵黄蛋白原（vtg）基因表达的影响,为Aroclor1254的毒性效应研究提供基础数据,以期选择Aroclor1254污染的敏感指标,进行早期污染监测和预警。[方法]将斑马鱼及其胚胎暴露在不同浓度的Aroclor1254溶液中,运用斑马鱼胚胎发育技术和组织病理观察法以及实时定量反转录聚合酶链反应（RT-PCR）检测Aroclor1254对斑马鱼胚胎发育的影响、形态学的改变和卵黄蛋白原（vtg）基因的表达。[结果]斑马鱼胚胎试验显示,3．3、6．5、10．0mg／L Aroclor1254等均可诱导肝变性、肝脏发育不全,其中3.3mg／L Aroclor1254诱导斑马鱼卵黄部分变性,6．5、10．0mg／L Aroclor1254诱导斑马鱼卵黄大部分或者全部变性。肝脏组织病理观察发现,2．0、10．0、50．0μg/L Aroclor1254肝细胞肿大,胞质疏松,空泡明显增加,细胞质中可见脂沉积。vtgmRNA的表达在Aroelor1254暴露的斑马鱼个体中产生了显著的改变,雌鱼中表达普遍呈抑制趋势,其中以2．0μg／L抑制现象最明显,而在雄鱼中该剂量组vtg表达量被显著诱导。[结论]研究表明Aroclor1254对斑马鱼及其胚胎具有毒性效应,肝脏是产生毒性效应的重要靶器官。     

氧乐果对小鼠睾丸特征性酶的影响及茶多酚的拮抗作用

目的研究有机磷农药——氧乐果对小鼠睾丸特征性酶的影响以及茶多酚对它的拮抗作用。方法将80只昆明雄性小鼠随机分成8组，即3个氧乐果染毒组，1个对照组，1个茶多酚组和茶多酚＋低、中、高剂量氧乐果染毒组。染毒组分别灌胃1、2、4mg／kg氧乐果；茶多酚组灌胃180mg／kg茶多酚；茶多酚＋低、中、高剂量染毒组小鼠提前灌胃茶多酚180mg／kg，2h以后分别灌胃1、2、4mg／kg氧乐果，对照组灌胃生理盐水，共灌胃6d。用比色法检测睾丸组织中睾丸特征性酶——碱性磷酸酶（AKP）、酸性磷酸酶（ACP）、乳酸脱氢酶（LDH）及乳酸脱氢酶X酶（LDH—X）的活力。结果随着氧乐果染毒剂量的增加，小鼠体重和睾丸重下降（P〈0，01或P〈0．05），睾丸AKP、ACP和LDH活力均升高（P〈0，05或P〈0，01）。预先灌胃茶多酚，2h后灌胃氧乐果，小鼠体重和酶活力有所变化，但与对照组比较，差异均无统计学意义（P〉0．05）。结论茶多酚对氧乐果所造成的小鼠睾丸特征性酶的影响有拮抗作用。     

稀土元素钬对小鼠3种抗氧化酶活力的影响

[目的]研究稀土元素钬对小鼠肝脏3种抗氧化酶活性的影响。找出剂量-效应关系。[方法]2次给小鼠腹腔注射氧化钬的盐酸溶液，相间24h，第2次注射24h后取肝脏检测超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）的活性，并进行统计分析，绘制出剂量-效应曲线。[结果]在10-40mg／kg体重剂量范围内3种酶的活性随剂量的增加而升高，40mg／kg体重酶活性达峰值，与阴性对照比较，t检验显示差异极显著（P〈0．01）；在40-160mg／kg体重剂量范围内3种酶的活性随剂量的增加而呈逐渐下降趋势。[结论]钬元素在低剂量下可能具有一定的抗氧化损伤作用，在高剂量时具有致抑制抗氧化酶活性的作用。     

Sediment TCDD-EQs and EROD and MROD Activities in Ranid Frogs from Agricultural and Nonagricultural Sites in Michigan (USA)

In vitro studies have demonstrated atrazine-mediated induction of 7-ethoxyresorufin O-deethylase (EROD) activity. EROD is an enzyme active in the metabolism of many compounds, including many xenobiotics. These studies have suggested that atrazine may affect reproductive function by altering steroid metabolism. The goal of this study was to determine whether relationships could be detected between measured atrazine concentrations in surface waters and the liver-somatic index (LSI) and EROD and 7-methoxyresorufin O-deethylase (MROD) activities in the livers of ranid frogs. In addition, sediment dioxin toxic equivalents (TCDD-EQs) were determined using the H4IIE-luc cell bioassay. Adult and juvenile green frogs (Rana clamitans), bullfrogs (R. catesbeiana), and Northern leopard frogs (R. pipiens) were collected from areas with extensive corn cultivation and areas where there was little agricultural activity in south central Michigan in the summer of 2003. Atrazine concentrations at nonagricultural sites ranged from less than the limit of quantification (0.17 μg atrazine/L) to 0.23 μg atrazine/L and did not exceed 1.2 μg atrazine/L at agricultural sites. Sediment TCDD-EQs were measurable only at one agricultural site. Of the measured parameters, only LSI values in adult male frogs differed significantly between agricultural and nonagricultural sites, with greater values observed at agricultural sites. In green frogs, EROD and MROD activities were measurable in both adult and juvenile frogs and were similar among sites. Median EROD activities ranged from 13 to 21 pmol/min/mg protein in adult male green frogs and from 5 to 13 pmol/min/mg protein in adult female green frogs. Juvenile frogs had greater EROD and MROD activities than adult frogs. Bullfrogs and leopard frogs had greater activities than did green frogs. Atrazine concentrations were significantly and negatively correlated with MROD activity in adult male green frogs (Spearman R = −0.800). LSI and EROD and MROD activities of adult female or juvenile green frogs were not significantly correlated with atrazine concentrations. These results suggest that atrazine does not appear to have a consistent association with EROD or MROD activities in wild-caught green frogs.     

Toxicokinetics of Atrazine in Embryos of the Zebrafish (Danio rerio)

Atrazine (2-chloro-4-ethylamino-6-isopropylamine-s-triazine) is a widely used selective herbicide. Due to its persistence, it is present in many surface waters, contaminating nontarget organisms such as fish. Teratogeny of atrazine was examined during the first 48 h of zebrafish development (embryo test) and correlated to effects on the microsomal and soluble glutathione S-transferases (m-/sGST; EC 2.5.1.18). Atrazine at 4 mg/L disturbed the normal development to long pec stage, at concentrations between 10 and 20 mg/L it caused retardations in organogenesis, a slowdown of movements, and functional disturbances of heart and circulatory system. m- and sGST activities were affected by atrazine in all investigated developmental stages. Atrazine elevated the mGST activity dose dependently up to a concentration of 5 mg/L, and the sGST up to 1 mg/L. Higher atrazine concentrations caused a decrease of GST activity, especially of the sGST of the younger stages, 32 cells and 75% epiboly. This might indicate that the detoxication system itself is affected, which then gives rise to morphological abnormalities during fish development. In vitro tests were performed to purify and characterize GST-formed atrazine metabolites by the use of ESI--HPLC--MS. mGST showed higher conversion rates compared to sGST.     

Uptake, toxicity, and effects on detoxication enzymes of atrazine and trifluoroacetate in embryos of zebrafish

The uptake, toxicity, and elimination of atrazine and trifluoroacetate (TFA) were studied in early life stages of the zebrafish (Danio rerio). Furthermore, the effects of these xenobiotics on soluble (s) and microsomal (m) glutathione S-transferases (GST) of zebrafish embryos were investigated using 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), and [(14)C]atrazine. [(14)C]Atrazine was taken up by the embryos within seconds, unhindered by the chorions. It accumulated in the embryos by a factor of 19 after 24 h of exposure time. LC(50) (48 h) was determined at 36.8 mg/L. At a level of 5 mg/L atrazine, activities of s and m GSTs were elevated in most stages, especially in prim 6 and long pec stage (24, 48 h after fertilization, respectively). GST activity toward atrazine was detectable only in untreated D. rerio eggs, increasing with developmental time. [(14)C]Atrazine was eliminated from the embryos between 24 and 48 h, indicating a possible metabolism to a more hydrophilic GSH conjugate. [(14)C]TFA was taken up by embryos, reaching at maximum fivefold the concentration of the incubation medium after 10 h. The chorions served no physiological protection. TFA (1 g/L) caused low elevation of the GST activity. No acute toxic effects (48 h) were observed up to 4 g/L TFA.     

Toxicity of lindane, atrazine, and deltamethrin to early life stages of zebrafish (Brachydanio rerio).

Fertilized eggs of zebrafish were exposed under flow-through conditions to several concentrations of the following pesticides: lindane 40, 80, 110, 130, and 150 micrograms/liter; atrazine 300, 1300, and 9100 micrograms/liter; deltamethrin 0.5, 0.8, and 1.2 micrograms/liter. Hatching, abnormalities in development (external deformations, edema, etc.), and mortality were recorded over a period of 35 days. At the end of the experiment, the body lengths of the fish were measured. Survival of juvenile fish after 35 days was reduced by increasing concentrations of all xenobiotics tested: lindane enhanced the mortality from 110 micrograms/liter and atrazine from 1300 micrograms/liter, and deltamethrin showed an effect even at the lowest test concentration (0.5 micrograms/liter). Other parameters were affected differently: hatching rate was reduced only by deltamethrin (from 0.8 micrograms/liter): lindane caused a decrease in growth (40 micrograms/liter) but had no effect on the other parameters. Atrazine increased the number of deformations and edema (1300 micrograms/liter) but did not influence hatching rate and growth. The sensitivity of the early life stages to the pesticides was compared with acute toxicity data (LC50) of adult zebrafish. The early life stages were less sensitive to lindane (118 versus 75 micrograms/liter), whereas in the case of atrazine (1300 versus 37,000 micrograms/liter) and deltamethrin (0.5 versus 2 micrograms/liter; 0.5 micrograms/liter was the lowest concentration tested) larvae were more sensitive.     

Phytotoxicity of Atrazine to Emergent Hydrophyte,Iris pseudacorus L.

The emergent hydrophyte Iris pseudacorus was constantly exposed over a 35-day period to atrazine in the laboratory. It could survive at an atrazine level up to 32 mg/L. Its relative growth rates were inhibited significantly when exposure dosage reached at or exceeded 2 mg/L (p < 0.05). No observed effect concentration and lowest observed effect concentration for growth were 1 and 2 mg/L, respectively. Chlorophyll a and b contents of the plant in all treatment groups were affected significantly, and chlorophyll a/b ratios of all atrazine treatment levels were pronouncedly higher than those of the control within 5 days of exposure (p < 0.05), but thereafter recovered to the level of the control. Differences of photosynthetic efficiency were significant between all atrazine treatments and the control; except for 1 mg/L on day 1 and 5, and 2 mg/L on day 1. I. pseudacorus did not show phytotoxicity symptoms after 35 days exposure to atrazine below 2 mg/L level, but photosynthetic efficiency had begun to decline.     

Reproductive and developmental effects of atrazine on the estuarine meiobenthic copepod Amphiascus tenuiremis

Atrazine is one of the most widely used herbicides in the United States. Atrazine concentrations in coastal environments chronically range from 90 ng/L to 46 microg/L, with rare but measured concentrations near 60 microg/L at edge-of-field conditions. Chronic atrazine effects on estuarine benthos exposed to environmentally relevant concentrations are unknown. The purpose of this research was to assess atrazine reproductive and developmental effects over multiple-generation exposures of the copepod Amphiascus tenuiremis. Copepods were chronically exposed to two environmentally relevant nominal atrazine concentrations (2.5 and 25 microg/L, and to an environmentally unrealistic concentration (250 microg/L). Chronic exposures were performed using a 96-well microplate life cycle bioassay. Individual stage I copepodites (C1, n = 60/treatment) were reared through two generations (F0 and F1) to sexual maturity and individually mated in microwells containing 200 microl of atrazine solution. Copepod survival across all treatments and generations was >95%. Atrazine did not affect development to reproductive maturity, time to egg extrusion, or time to egg hatch (p > 0.05). However, reproductive failures increased across generations with increasing atrazine concentrations. Reproductive failures in the 0-, 2.5-, 25-, and 250-microg/L atrazine treatments were 11, 11, 20, and 24% for the F0 and 4, 9, 26, and 38% for the F1, respectively. Compared to controls, total nauplii production per female was reduced by approximately 22% in F0 females exposed to 250 microg/L atrazine (p < 0.05), and by approximately 23%, approximately 27%, and approximately 32% in F1 females exposed to 2.5-, 25-, and 250-microg/L atrazine treatments, respectively (p < 0.05). The combined effect of reproductive failure and reduced offspring production significantly reduced total population growth in the F1 generation (p < 0.05) even at atrazine concentrations lower than that considered safe for seawater chronic exposure (26 microg/L).     

Interactions in the fate of chemicals in terrestrial systems

In outdoor lysimeters, [14C]atrazine (0.9 mg/kg dry soil), [14C]atrazine combined with the detergent n-dodecylbenzenesulfonate (0.9 and 10 mg/kg, respectively), [14C]n-dodecylbenzene-sulfonate (10 mg/kg), and [14C]n-dodecylbenzenesulfonate combined with atrazine (10 and 0.9 mg/kg, respectively) were applied to soils. Maize was grown in the first year and barley in the second year. n-Dodecylbenzenesulfonate increased the mobility of atrazine and its metabolites in soil as well as its leaching into water, its uptake by maize plants, and its volatilization from soil. Atrazine had a negative influence on mineralization, mobility in soil, leaching, plant uptake by both species, and binding rates of radiocarbon derived from the surfactant in soil and plants. The results were confirmed by short-term laboratory tests. Whereas the effects of the detergent on the fate of atrazine and its conversion products were apparent only in the first growing season, those of atrazine on the fate of detergent-derived residues could also be observed in the second year due to the persistence of atrazine in soil.     

Impact of Atrazine on Chlorpyrifos Toxicity in Four Aquatic Vertebrates

Atrazine has been shown previously to potentiate chlorpyrifos toxicity in selected invertebrates. This study examined interactions of atrazine and chlorpyrifos in four aquatic vertebrates. Organisms were exposed to binary mixtures of atrazine and chlorpyrifos during toxicity bioassays. Inhibition of cholinesterase (ChE) enzyme activity and chlorpyrifos uptake kinetics were also examined with and without atrazine exposure. Atrazine alone did not affect organisms at concentrations up to 5000 μg/L; however, the presence of atrazine at 1000 μg/L did result in a significant increase in the acute toxicity of chlorpyrifos in Xenopus laevis. Mixed results were encountered with Pimephales promelas; some bioassays showed greater than additive toxicity, while others showed an additive response. No effect of atrazine on chlorpyrifos toxicity was observed for Lepomis macrochirus and Rana clamitans. Atrazine did not affect ChE activity or chlorpyrifos uptake rates, indicating that these toxicodynamic and toxicokinetic parameters may not be related to the mechanism of atrazine potentiation of chlorpyrifos toxicity. Based on the results of this study, it does not appear that a mixture toxicity of atrazine and chlorpyrifos at environmentally relevant concentrations presents a risk to the vertebrate organisms examined in this study.     

The Effect of Creosote on Vitellogenin Production in Rainbow Trout (Oncorhynchus mykiss)

As part of a broader investigation into the effects of creosote treatments on the aquatic biota in pond microcosms, we examined the possible implications for vitellogenin (Vtg) production in Oncorhynchus mykiss [rainbow trout (RT)]. Vtg is the precursor of egg yolk protein and has emerged as a useful biomarker of exposure to estrogenic substances. Our a priori intent was to assess the ability of the creosote treatments (nominal cresoste concentrations were 0, 3, and 10 μl/L immediately after the last subsurface addition) to induce estrogenic responses in RT. The data showed no evidence of an estrogenic response in the treated fish. During the course of the experiment, however, the fish matured and began to produce Vtg, probably in response to endogenous estrogen. A posteriori analysis of the Vtg data from the maturing fish showed that after 28 days, the plasma Vtg concentrations were about 15-fold lower in fish from the creosote-treated microcosms compared with fish from the reference microcosm. Although the experiment design does not permit mechanistic insights, our observation suggests that exposure of female fish to PAH mixtures such as creosote can impair the production of Vtg with possible health implications for embryos and larvae.