The bioavailability of sediment-sorbed organic chemicals: A review

Xenobiotic chemicals that are present in aquatic environments are typically concentrated on suspended particles and sedimentary materials where they represent a source of chronic contamination to benthic and pelagic organisms. Laboratory and field studies of bioaccumulation, toxicity, and food-chain transfer of chemicals bound to sediment have shown the potential ecological impacts that may result from the contamination of sediments. In this review, the chemical and physical processes that determine the environmental fate of sediment-sorbed organic chemicals are outlined, and their relationship to bioavailability is discussed. Methods currently used to predict the fate of pollutants in the aquatic environment are of limited use for the assessment of sediment-sorbed chemical bioavailability because they are based on the compound's behavior in the water column. Furthermore, an organism's morphology and ecological niche can profoundly affect its ability to accumulate xenobiotic chemicals from sediments and these must be considered before the populations at greatest risk can be identified.     

Mutagenicity determination of the wastewater emitted from petrochemical industry in Taiwan

Thirty-eight wastewater samples were collected from 19 petrochemical plants located in Taiwan during 1991. These plants represented most of petrochemical industry in Taiwan. Water samples were passed through an XAD-2 resin column and then eluted by acetone. The mutagenicity of wastewater was determined by the Ames Salmonella/microsome test. 52.6 and 26.3% of wastewater collected respectively in summer and winter were found to exhibit mutagenic activity in Salmonella typhimuriumTA 98 and TA 100. Four samples collected from 2 plants had higher levels of mutagenicity. The measurement and identification of mutagenic pollutants in this kind of wastewater need further investigation.     

Plankton associations and related factors in a hypereutrophic lake

Cluster analysis was used to group samples collected from ten stations in Moses Lake, Washington, according to the similarity of their contained algal species. During the period 1968 to 1970, nine recurring distinct sample groups, or algal populations, were identified. Of the nine, three were most distinct; they consistently recurred at the same stations, and were dominated by diatom, green, and blue-green algae, respectively. Of the six species of blue-greens that characterized that population, the recreationally nuisance forms,Aphanizomenon flos-aquae andMicrocystis aeruginosa, were dominant. The blue-green population was the most widespread in the lake and occurred in waters that were warmest and contained the lowest concentrations of inorganic nutrients: N, P, and C. Green algae dominated in waters that received treated sewage effluent and contained relatively high concentrations of nutrients. As the nutrient content declined when proceeding away from that area, blue-green algae became dominant. Temporal variation in biomass (chlorophyll content) of the blue-green population was inversely related to phosphate content, but not to the other nutrients. These results support the hypothesis that nuisance blue-green algae dominate in shallow eutrophic lakes during warm summer months when ambient nutrient content is low because, under these conditions, they apparently out-compete other forms for nutrients. In shallow unstable eutrophic lakes like Moses Lake, the nutrient supply rate from sediments may be considered great although ambient concentrations are low which allow the dominating blue-green population to reach a large biomass, e. g., maximums as high as 300 µg l^?1 chlorophyll were observed. Because correlation analysis andin situ bioassays showed that biomass of blue-green algae was most closely related to inorganic phosphate even at times when nitrate was very low and invariable, we suggest that phosphorus availability is most critical to biomass formation. Control of ambient phosphorus content, therefore, would be most apt to result in a reduction in maximum biomass of the blue-greens. Phosphorus control would be unlikely to alter algal dominance in this shallow lake, however, since blue-greens seem to be generally favored over other populations by reduction in nutrient concentration during warm weather.     

Comparative genotoxicity testing of rhine river sediment extracts using the comet assay with permanent fish cell lines (rtg-2 and rtl-w1) and the ames test*

Goals, Scope and Background

Improved quality of surface waters and sediments requires advanced strategies for ecotoxicological assessment. Whilst at least in Germany assessment strategies on the basis of chemical analysis and acute toxicity data dominated the last decades, the development of more specific biological endpoints and biomarkers in ecotoxicology is required in order to arrive at a good ecological potential and good chemical status of surface waters in the European river basins until the year 2015, as required by the European Water Framework Directive. Since sediments have for long been known to function both as a sink and as a source of pollutants in aquatic systems, and since part of the particle-associated substances have frequently been demonstrated to cause mutagenic and carcinogenic effects in aquatic organisms, particularly in fish, there is, among other requirements, an urgent need to develop, standardize and implement integrated vertebrate-based test systems addressing genotoxicity into recent sediment investigation strategies. Thus, the present study was designed to compare the suitability of two commonly used test systems, the comet assay and the Ames test, for the evaluation of the ecotoxicological burden of surface and core sediment samples from the river Rhine.

Methods (or Main Features)

In order to determine the importance of inherent enzymatic activities, two permanent fish cell lines with different biotransformation capacities, RTL-W1 and RTG-2, were compared with respect to their capability of detecting genotoxic effects in 18 surface and core sediment samples from 9 locations along the River Rhine in the comet assay with and without exogenous bioactivation. For further comparison, as a prokaryotic mutagenicity assay, theSalmonella plate incorporation assay (Ames test) with the test strains TA98 and TA 100 with and without exogenous metabolic activation was used.

Results and Discussion

Whereas all sediment extracts induced genotoxic effects in the comet assay with RTL-W1 cells, only 12 out of 18 sediment extracts revealed significant genotoxicity in the tests with the less biotransformation-competent RTG-2 cells. Exogenous bioactivation by addition of ß-naphthoflavone /phenobarbital-induced S9 from rat liver resulted in both reduction or increase of genotoxicity in samples from different sites, however, without consistent reaction patterns. In general, the responses of RTL-W1 cells indicated higher biotransformation capacity than in RTG-2 cells without S9 complementation. In Ames tests using TA98 with S9, 16 out of 18 extracts induced significant mutagenicity with induction factors up to 4. Compared to TA98, the strain TA100 proved less sensitive, with maximum induction factors of 1.3, indicating the potential presence of substances inducing frarneshift mutations, which can only be detected in the strain TA98. Chemical analyses revealed particularly high levels of hexachlorbenzene (up to 860 µg/kg) and priority PAHs (up to 4.8 mg/kg); so far, however, no correlation could be found between compounds analyzed and the corresponding biotests.

Conclusions

Results document that both comet assay and Ames test are capable of detecting xenobiotic interaction with DNA in consequence of exposure to complex environmental samples. Whereas the alkaline version of the comet assay detects a broad range of interactions with the DNA, however without information about their eventual importance, the Ames test only reveals established mutations, but fails to detect transient (reparable) DNA alterations. However, even transient primary changes in the DNA structure might result in carcinogenic processes and, eventually, in implications at the population level. As a consequence, for hazard assessment purposes, a combination of both assays is required to avoid false negatives in genotoxicity evaluation. Poor correlation between data obtained by chemical analysis and results in bioassays is indicative of our limited understanding of the sources of genotoxicity. In fact, numerous studies combining chemical and biological approaches for hazard assessment of complex environmental mixtures indicate that priority pollutant concentrations are a poor indicator of toxicity.If compared to the cell line RTG-2, RTL-W1 proved more effective in detecting genotoxicity in surface sediment samples and, thus, indicated the importance of bioactivation of at least part of the compounds in superficial layers of sediments. Results further document that the common assumption may be wrong that, in comparison to deeper strata, surface layers carry a lower toxic burden in consequence of the current decrease in water pollution. This might at least in part be due to remobilization of more heavily polluted sediments from deeper layers during severe flood events followed by re-sedimentation in flood plains or upstream weirs, where they might cover less polluted younger sediment layers.

Recommendations and Perspectives

For a comprehensive assessment of genotoxicity in surface and core sediments, a combination of eukaryotic (comet assay) and prokaryotic assays (Ames test) with and without exogenous bioactivation is recommended. Since studies with organic sediments extracts simulate a worst-case scenario and fail to take into account bioavailability, there is broad consensus that whole-sediment exposure protocols represent the most realistic scenarios. Whereas more realistic solid phase exposure has frequently been applied in both microbial and invertebrate acute toxicity testing, there is an urgent need to develop corresponding whole sediment fish-based genotoxicity tests.

     

Pollution profile of a river

A host of chemical industries subject the river to pollutants such as acids, alkalies and their salts, trace metals and radionuclides belonging to the Th and U chains. Proximity of different outfalls and poor lateral mixing in the river are responsible for high local aquatic concentrations. Scavenging reactions, in situ, and sedimentation of suspended matter result in the accumulation of radionuclides near the outfall area. Monsoon ‘flushes out’ the river into the backwater area and translocation of sediments is the major factor in the transport of pollutants.     

Water and soil biotic relations in mercury distribution

The distribution of Hg is considered both in terms of its availability in soil fractions and the relationship between Hg in plant samples and Hg in ambient soils or other supportive media. The plants were grouped by habitat into epipedic-epiphytic (mosses, lichens) and endopedic-aquaticmarine (Basidiomycetes and algae) samples; non-vacular and vascular forms were also distinguished. Sources included Alaska, Hawaii, New England and Iceland. Brief consideration was also given to Hg distribution in a plant-animal-soil community. Data were expressed in terms of plant Hg content and plant substratum concentration ratio. Average Hg contents and concentration ratios, and modal ranges for the ratios were determined. The results showed similar average Hg contents in all groups (126 to 199 ppb) but a low value (84 ppb) in the lichens; terrestrial forms had ratios of 3.5 to 7.6 whereas the marine algae yielded a figure of 78.7. The modal ranges were 1 to 2 fold for mosses and lichens, 2 to 10 fold for Basidiomycetes and vascular plants and > 10 fold for algae. In addition to the modal ratio in the range 2–10 common to all 275 vascular plant samples, a secondary mode in the range 0 to 0.1 appeared only in the Alaska-New England group, over 500 km distant from active thermal sites. Thus evidence for both exclusion and concentration behavior was obtained.     

Atmospheric pollution and fallout by PCBS and organochlorine pesticides (Ile-De-France)

Air pollution and atmospheric deposition by PCBs and organochlorine pesticides (isomers of HCH and p,p′-DDE) were studied at Paris from January 1986 to June 1987. The deposition measured as total (wet plus dry) was also followed during 1986 on two suburban and two rural sites. The distribution of the pollutants between the vapor phase and aerosols was evaluated by sampling air through a glass microfiber filter connected to a Tenax resin cartridge. The study shows that in the atmosphere as in waters of the catchment area of the Seine river, PCBs are the main organochlorine pollutants. Pollution by OCL is of the same order as the one described in literature (mean γ-HCH concentration 1.4 ng m^?3) while PCB concentrations in the atmosphere are equal to or higher than those observed in USA and Europe (range 5 to 44 ng m^?3). On the average, 93% of the PCBs are in the vapor phase with a composition approximating Aroclor 1242. In aerosols and precipitations the composition is closely related to Aroclor 1254. The total fallout for 1986 was 40 μg m^?2 for PCBs and 20 μg m^?2 for γ-HCH, rainfall being 611 mm.     

The effects of three phthalate esters on the larval development of the grass shrimp Palaemonetes pugio (Holthuis)

The effects of three phthalic acid esters, dimethyl phthalate (DMP), di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) on survival and development rate of larvae of the grass shrimp Palaemonetes pugio were investigated. Only 100 ppm DMP and 10 to 50 ppm DBP were acutely toxic to the larvae. DMP at a concentration of 100 ppm significantly increased the duration of larval development to the first postlarval stage. DEHP concentrations up to 1 ppm (the solubility limit of this ester) were without effect on either survival or development rate of the larvae. Phthalate esters were not detectable at or above the 2 ppm level in the tissues of larvae chronically exposed to phthalates for the duration of larval development, suggesting active metabolism of phthalates by this species.     

The influence of the herbicide paraquat ‘Gramaxon’ on growth and metabolic activity of three chlorophytes

The acute toxicity of commercial herbicide, Paraquat was determined by 96-hr static bioassay on the freshwater chlorophytes Scenedesmus dimorphus (Trup.) Kuetz., Scenedesmus quadricauda (Trup.) de Brebisson and Ankistrodesmus falcatus (Cord) Ralfs. The 96-hr EC50 values of Paraquat for reducing growth and metabolic products of the three algae were determined. The number of days required for cell division increased with increasing Paraquat concentration. The three algae and their test parameters respond differently to Paraquat. Scenedesmus dimorphus was the most susceptible alga and the chlorophyll a was the most sensitive response parameter. On the other hand, the dry weight of the test algae was the most resistant parameter. It was observed that Paraquat has inhibitory effect on the primary producers.     

Comparison of avoidance responses of an estuarine fish,Fundulus heteroclitus,and crustacean,Palaemonetes pugio,to bis (tri-n-butyltin) oxide

Avoidance responses of an estuarine fish, mummichog (Fundulus heteroclitus), and crustacean, grass shrimp (Palaemonetes pugio) to the antifoulant his (tri-n-butyltin) oxide (TBTO) were evaluated. Four out of six groups of mummichogs tested at 1.0 μg total organic Sn L^?1 showed avoidance. Total organic Sn concentrations of ≥ 3.7 μg L^?1 were avoided by this fish species in all cases. Higher concentrations of total organic Sn did not result in greater avoidance responses. Grass shrimp did not avoid total organic Sn concentrations between 2.3 and 30.0 μg L^?1. Response data at 2.3 and 30 μg L^?1 were similar. Mummichogs and grass shrimp differed greatly in their abilities to avoid potentially adverse concentrations of total organic Sn. Since mummichogs are major predators of grass shrimp, these behavioral responses may have important implications for tidal marsh ecosystems.     

Ecotoxic impact of suspended solids collected from polluted surface waters

Scope and background

Earlier studies showed that artificially contaminated particulate matter could be responsible for acute effects in water fleas and fish. Physical/chemical measurements on suspended solids and river water collected in the field showed that these samples were often contaminated with mixtures of toxic molecules.

Objectives

The present pilot study was started to investigate the possible ecotoxic impact of suspended solids collected in situ.

Methods

Suspended solids and river waters were collected from 22 locations of polluted rivers in the Flanders. An extensive list of chemical components and physical parameters were measured in these matrices. Partition coefficients for water column and suspended solids were calculated. Toxicity of suspensions of solid materials was investigated in 3 test organisms of different trophic levels: Bacteria (BIOMET®), filter feeder (Daphnia magna) and fish (rainbow trout (Oncor-hynchus mykiss) or zebrafish (Danio rerio)). The acute toxicity was measured in a worst-case scenario using high concentrations of solids resuspended in standard medium and at standard conditions.

Results and discussion

The partition coefficients were highly variable, showing that this parameter is not simply related to the octanol/water partition coefficient or to the total organic carbon content of the solids in field conditions, as is often assumed in exposure models. The field material of some locations was toxic. Bacteria were the most sensitive test organisms, showing EC20 values at field relevant concentrations. For some samples, acute toxic effects were seen in fish and water fleas. The chemical content of the samples was very complex and could not simply be related to toxicity. Some samples were highly contaminated with toxic chemicals and yet caused no toxic effects, while other samples did not show extremely high concentrations, but were toxic to the test organisms.

Conclusions

Results show that biotests are needed, next to chemical measurements, to estimate the toxic impact of complex environmental matrices. A better understanding of the adsorption/desorption behaviour of toxic molecules in the water compartment and in living organisms will contribute to a better environmental risk assessment.

Recommendations and outlook

The results indicate that the ecotoxic impact of suspended solids in the field should be further investigated in realistic (non-worst-case) conditions, i.e. for chronic effects at field relevant concentrations. And more extensive scientific research is needed to understand the adsorption/desorption behaviour of toxic molecules in different physicochemical matrices.     

Field and laboratory studies of exposures of brown trout to acid waters

Some recent work on the effects of acid waters on brown trout are presented. Laboratory bioassay experiments have demonstrated that yearling trout are relatively insensitive to pH >4.3. Aluminium is demonstrated to be extremely toxic with suppression of growth occurring at concentrations above 20 μg L^?1 at pH 4.4 to 5.2. Aluminium toxicity is reduced at high pH (5.9 and 6.3). Field studies carried out on 61 acidic and circumneutral streams in upland areas of England and Wales showed a strong relationship between water quality and standing crop of 1+ brown trout. Measured pH levels per se were too high to be directly toxic. On the other hand, heavy metal and Al concentrations could account for low or zero brown trout biomass in the more acidic streams. A mobile bioassay laboratory has been developed to allow controlled bioassay experiments to be carried out in the field. Natural and synthesised waters can be tested concurrently in multi-factorial experiments with in situ determinations of pH, Ca, Al (total and monomeric) and other water quality characteristics.     

A hematoxylin staining technique to locate sites of aluminum binding in aquatic plants and animals

This paper describes a modified hematoxylin staining technique that can be used to locate sites of A1 binding in freshwater plants and animals. This technique is fast, simple, and inexpensive to use. It is more reliable for organisms raised under controlled conditions, although it can be used on organisms isolated from the field. In the presence of Al, a purple stain appears which absorbs between 560 and 570 nm. This stain can be used as a live stain over the pH range of 3 to 9. The stain remains stable for at least 12 mo in alcohol-preserved specimens. Low concentrations of Fe (reddish-brown) and high concentrations of Pb (grey) and Cu (pink) can mask the reaction with Al (purple). Fluoride (10:1 molar ratio to Al), EDTA (1:1 ratio to Al), humic acid and PO₄ (1:10 ratio to Al) can prevent A1 uptake or interfere with Al-hematein binding. Based on the technique described in this paper, sites of Al binding in aquatic plants and animals include: nucleus and cell wall of the green alga Mougeotia; cell wall of the aquatic moss Leptodictyum riparium; chloride cells, tip of the penis, and hind gut of the fairy shrimp, Branchinecta paludosa; and the anal papillae of the phantom midge, Chaoborus.     

Trace metals in a tropical river environment-distribution

Distribution of trace metals in the Periyar river has been investigated in detail. The fluvial concentrations of trace metals increase in river water and decrease in sediments during the summer months due to solubilization and concentration by evaporation. The levels, especially of Zn and Cd which are industrial pollutants increase by a factor of 10 both in water and sediments at the industrial zone. The concentration of Cd in the river water approaches the WHO standards for safe limits in drinking water. Solubilization at the backwater zone under high salinity is identified as one of the major mechanisms of trace metal transport to the marine environment. River meandering is responsible for large scale deposition of suspended solids at the industrial zone during the monsoon period. The trace metals exhibit build-up in specific concentration in the suspended solids in proportion to their residence time.     

Effects of acid mine wastes on aquatic ecosystems

The Cedar Creek Basin (39th N parallel 92nd W meridian) was studied for the period June 1952 through August 1954 to observe the effects of both continuous and periodic acid effluent flows on aquatic communities. The acid strip-mine effluent contained ferric and ferrous Fe, Cu, Pb, Zn, Al, Mg, titratable acid, and elevated H ion concentration, and was toxic to many of the aquatic organisms. In the areas of Cedar Creek, subjected to continuous acid flow, planktonic and benthic species had become adapted to the severe conditions and varied in abundance and diversity. No fishes were observed in the continuous acid effluents area. Downstream, where periodic mineral acid conditions changed drastically during an excessive effluent flow, planktonic and benthic communities had high diversity but low density. The populations of fishes were variable in this stream reach. The chemical basis of water quality variability was shown to be time-related, and statistically related to the aquatic communities. Physical, chemical and biological conditions of acid lakes formed by surface mining were reviewed. In addition to apparent physical and chemical differences in lakes, due in part to variable solar absorbance due to suspended oxides of Fe, chemical variability related to organic composition was reviewed. It is quite probable that degradation of such lakes can be reversed.     

土壤中溶解性有机质及其对污染物吸附和解吸行为的影响

溶解性有机质（DOM）已成为环境科学、生态学和土壤科学等学科的研究热点。DOM对重金属、养分和有机污染物的环境化学行为有很大影响,因此开展DOM与污染物（或养分）之间相互作用的研究,具有重要的理论与实践意义。本文系统地评述了DOM的来源、组成、分级及其对土壤中污染物吸附一解吸行为的影响。尽管关于土壤中DOM的研究还不完善,许多工作也只是刚刚开始,至今对土壤中DOM的性质、组成和分类方法等问题都不是很清楚,但现有的结果已经表明,DOM是土壤圈中一种十分活跃的重要化学组分,它对土壤中化学物质的溶解、吸附、解吸、吸收、迁移和生物毒性等行为均有显著的影响。     

The response of specific conductance to environmental conditions in the everglades National Park,Florida

The specific conductance of surface delivery waters to the Shark River Slough (Everglades National Park, Florida) has increased significantly since the completion of Levee 29 (L-29) and the S-12 water delivery system in the early 1960's. In order to document the response of specific conductance in the slough to changing environmental conditions, it was monitored continuously for a period of 12 mo at a location in central Shark approximately 17 km south of the water delivery site. In addition, variability in isoconductivity patterns throughout the slough was assessed by conducting biweekly surveys at 97 locations. Specific conductance was found to respond to a variety of natural and manmade environmental changes and proved to be an important management tool serving as an early indicator of potentially broad changes in water quality. Factors important in determining overall isoconductivity patterns in Shark Slough include:

1. the ionic composition of surface delivered to Shark Slough via the S-12 delivery structures.
2. the quantitative relationship between the amount of surface water delivered to the slough and the amount of precipitation falling directly upon the slough.
3. the effects of evapotranspiration and concentration of biological organisms during seasonal periods of extreme drawdown.

     

Effects on soil properties of vertic movements in Calcisols from southern Spain

The analytical, mineralogical and micromorphological characteristics of Calcisols are studied here, in order to improve their genesis and influence in soil properties. Two main features stand out: one being of a colluvial nature, consisting molasses and bioclastic molasses (postorogenic marine detrital sediments whose origin is the upper-middle Miocene) over primitive haplic Vertisols, with appearance of subsurface gilgai microrelief, non visible from the ground and, the other, being the appearance of a calcic horizon resulting from the leaching and translocation of carbonates proceeding from the colluvial material. The former Vertisol had suffer an erosion process which removed its A horizon and later was produced new material deposition. The deposited carbonated material was loose, becoming soils in Calcisols. As a result of the vertic movements, the subsurface gilgai in the boundary between the new deposited and former material, which remains buried, show the higher degree of undulation in front of non buried Vertisols, by polynomial equations.     

Pollution dynamics of different components of forest ecosystems with 137Cs in Bryansk,woodlands

The features in the redistribution of ¹³⁷Cs and its chemical analog ³⁹K in the structures of the main forest forming tree species (pine and birch) of Bryansk’s woodlands in the remote period after the Chernobyl fallout are considered. The dynamics of the specific activity of ¹³⁷Cs in these structures is analyzed. Some differences in the redistribution of ¹³⁷Cs and ³⁹K in the components of pine and birch, as well as their long-term dynamics, were revealed.     

Synergistic effects of heavy metal pollutants on senescence in submerged aquatic plants

The effects of many combinations of toxic concentrations of heavy metal pollutants, viz., mercuric chloride, lead acetate, cadmium chloride and cupric sulphate, on the senescence of isolated mature leaves of submerged aquatic plants, Potamogeton pectinatus L., Vallisneria spiralis L., and Hydrilla Verticillata (L.f) Royle were studied. All of the combinations of heavy metal pollutants caused senescence in all three species by decreasing chlorophyll, DNA, RNA, protein and dry wt, and increasing free amino acid, tissue permeability, the activities of protease and RNase, and the ratio of acid to alkaline pyrophosphatase activity over control values. The effects were highest in Potamogeton and lowest in Hydrilla. The degree of senescence in the three submerged plants by combinations of toxic concentrations of heavy metal pollutants is much higher due to synergism than that by individual heavy metal pollutants.