Determination of total petroleum hydrocarbons and heavy metals in soils within the vicinity of facilities handling refined petroleum products in Lagos metropolis

This article discusses the determination of total petroleum hydrocarbons (TPH) and heavy-metal contamination in soils within areas of refined petroleum products handling in Lagos metropolis. Soil samples were collected randomly from two petrol stations, two auto-mechanic workshops, and a National Electric Power Authority (NEPA) station. Control samples were taken from two low-density residential areas. TPH were estimated gravimetrically following standard methods of TPH analysis, while the heavy metals were determined by atomic absorption spectrophotometry. Sites studied had higher levels of TPH and heavy metals compared to the control samples. For TPH, the petrol stations have mean values of 399.83+/-106.19 and 450.83 +/- 90.58 microg/g, respectively; mechanic workshops, 362.60 +/- 185.84 and 428.55 +/- 119.00 microg/g, respectively; while the NEPA station has 356.20 +/- 210.30 microg/g compared to the control mean of 26.63 +/- 4.58. It revealed that the improper handling of refined petroleum products are potential sources of soil contamination in the sampled sites. This is indicated by the statistically significant levels of TPH and heavy metals observed between the control samples and those collected from the petroleum products handling sites. Bioremediation using microorganisms and plants is recommended.     

月湖底栖动物的空间格局及其对水草可恢复区的指示

底质适宜是富营养湖泊恢复沉水植物(水草)的重要前提。大型底栖动物可综合指示底质的污染程度，于2002~2003年在武汉月湖开展了底栖动物水平分布对水草可恢复区指示作用的研究。首先通过月湖底栖动物与环境的相关分析，选择颤蚓科寡毛类作为底质营养状况的指示类群，然后利用同类湖泊群颤蚓与水草数据分析阈值，初步确定颤蚓密度≤100 ind/m2的底质适合水草生长，最后绘制月湖颤蚓分布的水平等值线，显示水草恢复的合适区域。在此基础上构建了应用底栖动物空间格局指示水草恢复区的技术原理框架。     

Sedimentation rates and trace metal input history in intertidal sediments from San Simón Bay (Ría de Vigo, NW Spain) derived from 210Pb and 137Cs chronology

(210)Pb and (137)Cs dating methods, accompanied by a high-resolution geochemical study, were applied to intertidal sediments containing both fine and coarse-grained particles and also, anthropogenic Pb in order to establish sedimentation rates and historical trends in heavy metal input. Sedimentation rates were established according to the "Constant Flux:Constant Sedimentation" (CF:CS) (210)Pb dating model, which was preferred rather than the "Constant Rate of Supply-Minimum Variance" (CRS-MV) model. Variations in sediment grain-size were accounted for by application of several normalization procedures. Al was selected for grain-size correction. Corrected sedimentation rates obtained from (210)Pb dating were corroborated through a second independent radionuclide tracer and by comparison of peak trace metal inputs into the environment with peaks in the sediment. The Chernobyl maximum was identified in the normalized (137)Cs activity profile. Sedimentation rates of 6.2+/-1.2 mm y(-1) and 3.1+/-0.5 mm y(-1) for the upper (two muddy layers) and 6.0+/-2.0 mm y(-1) for the lower (sandy) intertidal mud flat deposits of San Simón Bay were determined. According to the established chronology, human-induced environmental changes were detected in total metal concentrations (Cu, Pb, Zn) and in sediment grain-size and composition.     

Sediment integrative assessment of the Bay of Cádiz (Spain): An ecotoxicological and chemical approach

This study consisted of the sediment toxicity assessment of the Bay of Cádiz based on two endpoints: growth inhibition for Cylindrotheca closterium (benthic microalgae) and fecundity inhibition for Tisbe battagliai (harpacticoid copepod). A new methodology to eliminate (but not as storage technique) the autochthonous biota present in the sediment samples by immersing them in liquid nitrogen (? 196 °C) was also assessed. Sediment toxicity data showed different toxicity levels for both organisms. In general, T. battagliai was more sensitive; however a good correlation (r = 0.75; p  < 0.05) between sediment toxicity results for both species was found. Data in pore water (pH, redox potential, and toxicity for microalgae and copepod) and sediment (pH, redox potential, organic carbon, and metal concentrations) demonstrated that ultra-freezing did not alter sample characteristics; thus, this technique can be adopted as a pre-treatment in whole-sediment toxicity tests in order to avoid misleading results due to presence of autochthonous biota. Multivariate statistical analysis such as cluster and principal component analysis using chemical and ecotoxicological data were employed. Silt and organic matter percentage and lead concentration were found to be the factors that explain about 77% of sediment toxicity in the Bay of Cádiz. Assay methodology determined in this study for both assayed species is considered adequate to be used in sediment toxicity monitoring programs. Results obtained using both species show that the Bay of Cádiz can be considered a moderately polluted zone.     

Spatio-temporal variation of macrobenthic communities in the mangrove-fringed Segara Anakan lagoon, Indonesia, affected by anthropogenic activities

The benthic macrofauna of the Segara Anakan lagoon, Java, Indonesia and its fringing mangroves were investigated between May 2004 and August 2006. This lagoon has been affected by various human activities for decades, in particular fishing, effluents from agriculture and industry, and illegal deforestation. In total, 163 taxa were identified, including 127 species occurring in the mangrove forest and 59 species in the subtidal. Mean density of macrobenthos was 2.5-fold higher in the central (881.8 ± 1,151.3 ind. m^?2) than in the eastern mangrove site (356.3 ± 218.8 ind. m^?2). Community structures differed significantly between these sites and showed a serial shift during the investigation period. Gastropods dominated the community in the central mangrove location, whereas sipunculids, polychaetes and gastropods had similar densities in the eastern site. Differences in community composition were best explained by three sediment properties: pore water salinity, δ¹³C_org, and C_org/N. It is suggested that small-scale heterogeneity of food availability and quality is a main factor determining the small-scale variability of the community composition. Compared to other Indo-West Pacific mangroves, species richness and densities are high. However, the dominance of specific taxa, especially of opportunistic species and the comparably low species richness in the subtidal of the lagoon may be attributed to the high sediment input by rivers in the central part and to the large-scale cutting of mangroves. Continuous tree logging will probably lead to a further spread of two fast growing understorey plants and thus to an increase of uniform swamp sites and a decrease of micro-habitats for benthic macrofauna. To our knowledge, this is the first detailed study on the spatio-temporal variation of benthic macrofauna in mangroves of Indonesia.     

Screening ecological risk assessment for the benthic community in the Venice lagoon (Italy)

According to the risk hypothesis: the sediment as source of potential risk for the benthic community, an Ecological Risk Assessment (ERA) based on the quotient method was undertaken. The exposure of the benthic community to different classes of pollutants (metals, chlorinated organic compounds and polynuclear aromatic hydrocarbons) was inferred by estimating the pollutant stocks in the top 15-cm sediment of the whole Venice lagoon, after application of geostatistic techniques. The risk was calculated by comparing the sediment exposure profiles with the ecotoxicological benchmarks for benthic organisms. Kriging based maps of the spatial distribution of the estimated risk for the benthic community over the whole lagoon were obtained. The highest risk, found in the areas nearest to the sources of contamination (e.g., the industrial district of Porto Marghera and the river mouths), was posed by mercury (40% of the sampling stations showed exposure levels higher than the Probable Effect Level), arsenic and nickel (75% of the sampling stations exceeded the Threshold Effect Level).     

Concentrations of Cu and Pb in the offshore and intertidal sediments of the west coast of Peninsular Malaysia

Malaysia is now a developing country and on her way towards being an industrialised one by the year 2020. Most of her industries and urban areas are located on the west coast of Peninsular Malaysia. In addition, the offshore area of the west coast is now one of the busiest shipping lanes in the world. These two phenomena make the intertidal and offshore areas of the west coast of Peninsular Malaysia interesting for scientific studies. Therefore, this study focused on both the offshore and intertidal sediments of the west coast of Peninsular Malaysia. Sampling for sediment samples were done from the northern to the southern ends of the peninsula and these sediment samples were analysed for Cu and Pb. It was found that total Cu concentrations ranged from 0.25 to 13.8 and 0.40 to 315 microg/g dry weight (dw) for offshore and intertidal sediments, respectively. For Pb, it ranged from 3.59 to 25.4 and 0.96 to 69.8 microg/g dw for the offshore and intertidal sediments, respectively. The ranges of Cu and Pb found from the west coast of Peninsular Malaysia were low in comparison to regional data. However, some intertidal areas were identified as receiving anthropogenic Cu and Pb. Geochemical studies revealed that the 'nonresistant' fraction for Pb contributed about 70.0% to 75.0% and 54.0% of the total Pb concentration in the offshore and intertidal sediments, respectively. As for Cu, the 'nonresistant' fraction contributed about 46.2% to 60.4% and 46.3% of the total Cu concentration in the offshore and intertidal sediments, respectively. The 'nonresistant' fraction contained mostly of anthropogenic metals besides natural origins. These 'nonresistant' percentages indicated that both the offshore and intertidal areas could have received anthropogenic-derived metals, which could be influenced by physico-chemical properties of the sediments. Although the present data indicated that contamination due to Cu and Pb in the west coast of Peninsular Malaysia especially in the offshore areas were not serious, regular biomonitoring studies along the west coast of Peninsular Malaysia are recommended.     

Benthic fauna in relation to pollution: A case study at River Chambal near Kota in Central India

The Chambal river, subjected to industrial and sewage pollution, was studied with reference to the benthic fauna. Twenty seven taxa of benthic fauna of four main groups were observed at the stretch of the river: Oligochaeta, Diptera, Mollusca and Insecta (“others”). It was noted that the pollution input zone shows less fauna. The analysis of various physicochemical parameters showed an increase in pollution where domestic and industrial effluent were added. Changes in the benthic community have been explained with the help of the Diversity Index. The species diversity values showed a decrease from the prepollution point to the effluent discharge channel with an increase at the posteffluent point, indicating it to be a recovery zone. The coefficient of correlation was assessed between different physicochemical and different groups of benthic fauna.     

基于知识的洞庭湖湿地遥感分类方法

湿地遥感影像分类是遥感研究的一大难题。分析洞庭湖不同湿地类型在遥感影像上的光谱曲线规律,利用两个季节的洞庭湖ETM数据,并辅助以物候特征和地面GIS信息,通过遥感软件Erdas Image的专家分类知识库建立决策树分类方法,结合研究区的DEM进行洞庭湖湿地的影像分类,通过专家分类器分层次实现了包括水体、泥沙滩地、防护林滩地、湖草、芦苇滩地和苔草滩地以及其他水体7种湿地类型的分类。相比传统分类方法,专家分类过程以规则为基础,可以同时利用多个条件进行分类,减少了数据处理时间,同时还提高了分类精度,最终得到试验区较为可靠的遥感分类图像。     

Benthic community structure and biomarker responses of the clam Scrobicularia plana in a shallow tidal creek affected by fish farm effluents (Rio San Pedro,SW Spain)

The effects of solid organic wastes from a marine fish farm on sediments were tested using benthic community as ecological indicators and biomarkers in native clam (Scrobicularia plana) as biochemical indicators. The benthic fauna and clam samples were collected in the intertidal sediment in October 2010 from five sites of the Rio San Pedro (RSP) creek, following a gradient of contamination from the aquaculture effluent to the control site. Numbers of species, abundance, richness and Shannon diversity were the biodiversity indicators measured in benthic fauna. Morphological and reproduction status of clams were assessed using the condition factor and gonado-somatic index, respectively. Phase I and Phase II detoxification enzymatic activities (ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST)), antioxidant enzymatic activities (glutathione peroxidase (GPX), glutathione reductase (GR)) and oxidative stress parameters (Lipid Peroxidation (LPO) and DNA strand breaks) were measured in clams' digestive gland tissues. In parallel, temperature and salinity in the adjacent water, redox potential, pH and organic matter in sediment, and dissolved oxygen in the interstitial water were measured. The results suggested that RSP showed a spatial gradient characterised by hypoxia/anoxia, reduced potential, acidic conditions and high organic enrichment in sediments at the most contaminated sites. Significant (p < 0.05) decrease of biodiversity indicators were observed in the areas impacted by the aquaculture discharges. Biomarkers did not show a clear pattern and of all biochemical responses tested, GPX, DNA damage and LPO were the most sensitive ones and showed significant (p < 0.05) increase in the polluted sites. Benthic biodiversity indicators were significantly (p < 0.05) positively correlated with pH, redox potential and dissolved oxygen and negatively correlated with organic matter. On the contrary, antioxidant enzymatic responses (GPX) and oxidative stress parameters were significantly (p < 0.05) negatively correlated with those physico-chemical parameters. It has been demonstrated that effluents from fish aquaculture activities in Río San Pedro creek may produce an alteration of physico-chemical characteristics of seabed and induce oxidative stress and DNA damage in soft-sediment species which may lead to changes of the benthic population structure and health status of the exposed organisms.     

不同滩涂促淤围垦方式对大型底栖动物群落的影响

滩涂促淤围垦会对大型底栖动物造成一定程度的影响,但关于不同促淤方式对大型底栖动物的影响未见有报道。以长江口浦东机场外侧滩涂促淤区为研究对象,分析吹沙促淤区域和抛坝促淤区域中大型底栖动物的分布特点。结果显示:大型底栖动物在抛坝促淤区和吹沙促淤区年均密度分别为(835.98±572.41)ind./m~2和(52.85±12.04)ind./m~2,年均生物量分别为(135.25±63.99)g/m~2和(40.82±6.84)g/m~2,单因素方差分析显示,两者存在显著性差异(P0.05),进而表明不同促淤方式对大型底栖动物的密度和生物量影响不同。CLUSTER聚类和MDS排序图说明吹沙促淤区和抛坝促淤区断面之间的大型底栖动物群落组成存在差异性。对各断面间群落相似性矩阵进行SIMPER分析表明河蚬、光滑狭口螺和谭氏泥蟹为两种区域共有优势种,其贡献度分别为56.10%、10.81%、9.62%,且三者在吹沙促淤区中的密度分布少于抛坝促淤区。研究表明泥沙淤积的快慢程度是影响促淤围垦区内大型底栖动物分布的重要因素。     

近期长江口崇明岛周边岸滩沉积特征及影响机制

大河入海河口由于巨量泥沙堆积以及潮汐作用,往往发育着河口沙岛。崇明岛是世界上典型的河口沙岛,近年来,随着长江流域泥沙来源锐减以及河口大型水利工程建设等,给崇明岛周边岸滩沉积环境带来深刻影响。研究依据2015年9月～2018年4月对崇明岛周边14个岸滩断面的表层沉积物采样数据和定点水文观测资料,分析崇明岛周边岸滩沉积环境特征和区域性差异,探讨不同岸滩断面沉积过程和作用机制。结果表明:崇明岛岸滩沉积物以砂质粉砂和粉砂质砂为主,沉积物中值粒径总体表现为南岸北岸东滩,平均为48μm。南、北岸岸滩总体表现为坡陡、滩窄,沉积物自西向东逐渐变细的特征,北岸岸滩坡度略缓,南岸崇头至庙镇之间存在局部细颗粒物质沉积区;东部岸滩滩宽、坡缓,整体表现为"北细南粗"的沉积特征。岸滩沉积断面上,上细下粗,高潮滩处粘土组分含量相对较高,水下斜坡和河槽底部粉砂含量较高。南、北支河势演变形成了崇明岛"南坍北涨"沉积环境的分布格局;径、潮流作用对岸滩断面沉积物分布特征影响明显;风浪对崇明东滩浅滩沉积物具有强烈的分选作用;潮滩植被主要影响细颗粒沉积物在潮间带的分布;流域来沙减少对崇明东滩前沿沉积环境趋势影响显著。     

A phytochelatin-based bioassay in marine diatoms useful for the assessment of bioavailability of heavy metals released by polluted sediments

The aim of the present work was to develop a new bioassay involving the presence of phytochelatins (PCs), detoxifying intracellular metal-binding peptides, in microalgae as response to metal bioavailability in re-suspensions of metal-polluted marine sediments. For this purpose, the synthesis of PCs has been studied in laboratory cultures of three marine diatoms, namely Phaeodactylum tricornutum, Thalassiosira weissflogii and Skeletonema costatum, exposed to elutriates of sediments collected in a polluted coastal area in the province of Pisa (Tuscany, Italy). Short- and long-term incubations in the elutriates of two marine sediments (named A and B) exhibited an increase of PCs synthesis in all the phytoplanktonic species examined, when the elutriate concentration increased from 0% to 100%. Elutriate B, which was mainly contaminated by Cd, was shown to be more effective to induce PCs than elutriate A, which was richer in Cu and TOC. The results show that the PCs response, in the microalgae examined, was species-specific. Our data also show that the PCs synthesis occurred before the growth rate was affected, thereby indicating that PCs can be considered as an early warning response of metal exposure. The PCs response in exponentially growing cultures of T. weissflogii, which was found to be the most sensitive alga, increased when the initial cellular density decreased. Finally, the positive relationship obtained between the cellular PCs concentration in T. weissflogii and the degree of metal contamination of the elutriates from twelve sediments collected in a metal-polluted coastal area, confirmed that the PCs-induction test can be applied in field studies. In conclusion, the response of these marine microalgae suggests that these cellular peptides could represent an excellent biomarker of metal exposure, which is useful for the assessment of sediment toxicity, by carrying out PCs-induction tests on sediment elutriates.     

长江口潮滩沉积物中活性重金属的空间分异及控制机制

利用盐酸羟氨-25%醋酸溶液，提取了长江口潮滩沉积物中活性重金属含量。研究发现，长江口潮滩沉积物中活性重金属占总量的百分含量依次为Cu 26%，Pb 36%，Fe 7%，Mn 49%，Zn 32%，Cr 14%和Al 16%，沉积物基本未受到Cr污染，其余重金属污染程度处于中等偏下水平。除Zn、Cr外，其余活性重金属在夏季沉积物中的含量明显低于春季，其主要原因是夏季风暴潮将大量细颗粒泥沙及其富集的重金属带离潮滩进入了河口水体中。受点源污染排放及沉积物粒度影响，活性重金属在长江口南岸的浒浦、顾路和浦东机场出现峰值含量，且高潮滩含量明显高于中、低潮滩。在垂向上，重金属一般在沉积物表层或亚表层形成富集。在口门附近的滨岸潮滩沉积物中，Cu、Pb的空间分异主要受早期成岩作用的控制，在污染较为严重、水动力作用相对较弱的潮滩沉积物中，Cu、Pb的空间分异主要受沉积物中有机质含量变化的控制.     

Gamma dose rates and distribution of natural radionuclides in sand beaches--Ilha Grande, Southeastern Brazil

In order to study the process of dispersion and the activity concentration of 232Th and 238U series and 40K radionuclides in two island beaches in southeastern Brazil, analyses was made of sand samples of 0-10 cm profile, during a 12-month period. Moreover, the monthly variations of gamma dose rates were studied to determine the local environment absorbed dose rate. The average activity concentration of primordial radionuclides 232Th, 238U and 40K at Preta beach, they were 239, 121 and 110 Bq kg(-1), while at Dois Rios beach they were 48, 39 and 412 Bq kg(-1), respectively. The absorbed dose rate in air, observed at 1 m above the ground, ranged from 54 to 228 nGy h(-1) at Preta beach and from 39 to 110 nGy h(-1) at Dois Rios beach. The annual effective dose equivalent corresponding to Preta beach is 0.15 mSv a(-1) and to Dois Rios 0.08 mSv a(-1).     

Environmental impact studies of barium and radium discharges by produced waters from the "Bacia de Campos" oil-field offshore platforms,Brazil

Produced water samples from different E&P offshore petroleum platforms, belonging to the Bacia de Campos oil field, Brazil, were analyzed for barium, 226Ra and 'Ra. The concentrations measured are in the range of 0.36-25.7 mg l(-1) for barium, 0.012-6.0 Bq l(-1) for 226Ra and <0.05-12.0 Bq l(-1) for 1Ra. A strong correlation between the concentration of barium and radium isotopes was observed (226Ra: r2=0.926: 228Ra: r2=0.785). Additionally, seawater and sediment samples were taken at different distances (from 250 to 1,000 m) from the two selected platforms. Water samples were analyzed for dissolved and particulate barium, 226Ra and 225Ra and the sediment samples for total and leachable barium, 226Ra and 228Ra. The results showed that even for the shortest sampling distance (250 m) from the discharge point, barium, 226Ra and 228Ra concentrations are similar to the local background, indicating that dispersion by local currents is enough to minimize environmental impacts.     

Inputs and fates of petroleum hydrocarbons in a subtropical marine estuary

Inputs and fates of petroleum from a higly urbanized area to a subtropical marine estuary were investigated by measuring hydrocarbon concentrations in municipal wastewater treatment plants, urban stormwater drains, sediments, and benthic organisms in and around Tampa Bay, FL. The concentrations of petroleum hydrocarbons discharged from secondary and tertiary treatment plants in this area were lower than concentrations previously reported for other treatment plants in temperate regions. Samples collected from urban storm drains under base flow conditions were also low. The generally low levels of petroleum hydrocarbons in the sediments and organisms throughout Tampa Bay suggest that the bay is relatively pristine with respect to petroleum hydrocarbon contamination. Since it is unlikely that the anthropogenic input of hydrocarbons to this estuary is significantly lower than in other urbanized areas, we suggest that elevated annual temperatures in this subtropical system result in increased metabolic rates of microorganisms and more rapid degradation or metabolism of the petroleum hydrocarbons.     

Spatial distribution of arsenic in the intertidal sediments of River Scheldt, Belgium

A study was carried out to assess the spatial distribution of arsenic in the intertidal sediments of the River Scheldt in Belgium. Sediment samples were collected from different locations along the River Scheldt up to 100 cm depth and analysed for the major physicochemical properties. The study reveals that the arsenic contents in the sediment samples vary in a wide range, from 2.3 to 140.2 mg kg(-1) dry weight. Moreover, the arsenic concentrations are generally below the background concentrations and remediation thresholds of arsenic in Flanders, Belgium. The occurrence of arsenic is found closely related to some physicochemical properties of the sediments. Arsenic has a strong positive correlation with organic matter and clay contents. On the contrary, a negative correlation exists between arsenic, sand and pH. It is recommended to develop and use organic matter control practices for lowering further accumulation of arsenic within the sediments.     

Dike Breach Risks of Different Flood Conditions in the Lower Yellow River

Based on the analysis of hanging rivers' actuality in the lower Yellow River and researches related to the evaluation of dike breach risks, it is put forward that the influencing factors of dike beach risks in the lower Yellow River should involve four aspects, the flow and sediment movement, the regional crustal stability, the variation of river regime and the stability of river dikes. With this, the evaluation indexes system of dike breach risks is established, and with the support of geographic information systems technology, the model of multi-hierarchical fuzzy comprehensive judgment is applied to estimate the dike beach risks of the hanging rivers in the lower Yellow River under different flood conditions. The evaluation results of dike breach risks show the following distributing regularities of dike breach risks in the lower Yellow River: (1) Dike breach risks increase with the increase of the flood. (2) Dike breach risks decrease with the changes of river patterns along the channel. (3) There are great risks of dike breach in the wandering reaches, and it is relatively higher in the south bank than in the north in wandering reaches. (4) There is a higher dike breach risk in the north bank than in the south in winding reaches. Simultaneously, the evaluation results manifest that the evaluation indexes system established from the flow and sediment movement, the regional crustal stability, the variation of river regime and the stability of river dikes can represent the actual situation of the lower Yellow River more comprehensively. The application of multi-hierarchical fuzzy comprehensive judgment can preferably resolve the problem of hanging river dike breach, which has numerous influencing factors and complicated functionary mechanisms. The applications of geographic information systems technology with powerful spatial analysis functions make dike beach risks quantificationally displayed in different spatial positions, and reflect the differences of dike beach risks in different spatial positions of the channel in the lower Yellow River.     

An estimation of radiation doses to benthic invertebrates from sediments collected near a Canadian uranium mine.

A new method is described for calculating radiation doses to benthic invertebrates from radionuclide concentrations in freshwater sediment. Both internal and external radiation doses were estimated for all 14 principal radionuclides of the uranium-238 decay series. Sediments were collected from three sites downstream of a uranium mining operation in northern Saskatchewan, Canada. Sediments from two sites, located approximately 1.6 and 4.4 km downstream from mining operations, yielded absorbed doses to both larval midges, Chironomus tentans, and adult amphipods, Hyalella azteca, of 59-60 and 19 mGy/year, respectively, compared to 3.2 mGy/year for a nearby control site. External beta radiation from protactinium-234 (234Pa) and alpha radiation from uranium (U) contributed most of the dose at the impacted sites, whereas polonium-210 (210Po) was most important at the control site. If a weighting factor of 20 was employed for the greater biological effect of alpha vs. beta and gamma radiation, then total equivalent doses rose to 540-560 mGy/year at the site closest to uranium operations. Such equivalent doses are above the 360-mGy/year no-observed-effect level for reproductive effects in vertebrates from gamma radiation exposure. Data are not available to determine the effect of such doses on benthic organisms, but they are high enough to warrant concern. Detrimental effects have been observed in H. azteca at similar uranium concentration in laboratory toxicity tests, but it remains unclear whether the radiotoxicity or the chemotoxicity of uranium is responsible for these effects.