Polychlorinated biphenyls and DDT alter species composition in mixed cultures of algae

A lentic microcosm approach to determine the toxicity of DDT and deltamethrin on diatom communities

Worldwide the use of pesticides has increased, especially in the industry and agriculture sector even though they contain highly toxic substances. The use of pesticides has various negative effects on the aquatic ecosystem and organisms within these ecosystems. The paper aimed to assess the effects of increased concentrations of malaria vector control insecticides (Dichlorodiphenyltrichloroethane (DDT) and Deltamethrin (DTM)) on the freshwater diatom community structure using a microcosm approach as well as determine whether a mixture (DDT 1:1 Deltamethrin) exposure will have a greater influence on the diatom community when compared to single exposures of these insecticides. Diatoms were exposed to a high and low concentration (based on LC50 data for freshwater Xenopus laevis from the USEPA Ecotox database) of DDT, DTM and a mixture in lentic microcosms over a total period of 28 days. Results indicated that irrespective of exposure concentrations, DDT, DTM and a mixture had negative effects on the diatom community including functionality and vitality as these insecticides induced changes to their chloroplasts. There was an increased percentage dead cells for all exposures compared to the control, with the insecticides having a phototoxic effect on the diatom community. Exposure to the selected insecticides caused a significant decrease in some diatom metrics indicating the negative effects these insecticides have on the diatom metrics. Therefore, diatoms may prove to be useful as bio-indicators in ecotoxicology studies when assessing the effects of any insecticide exposures.

Ecological effects of various toxic agents on the aquatic microcosm in comparison with acute ionizing radiation

The purpose of this study was an evaluation of the effect levels of various toxic agents compared with acute doses of ionizing radiation for the experimental model ecosystem, i.e., microcosm mimicking aquatic microbial communities. For this purpose, the authors used the microcosm consisting of populations of the flagellate alga Euglena gracilis as a producer, the ciliate protozoan Tetrahymena thermophila as a consumer and the bacterium Escherichia coli as a decomposer. Effects of aluminum and copper on the microcosm were investigated in this study, while effects of gamma-rays, ultraviolet radiation, acidification, manganese, nickel and gadolinium were reported in previous studies. The microcosm could detect not only the direct effects of these agents but also the community-level effects due to the interspecies interactions or the interactions between organisms and toxic agents. The authors evaluated doses or concentrations of each toxic agent which had the following effects on the microcosm: (1) no effects; (2) recognizable effects, i.e., decrease or increase in the cell densities of at least one species; (3) severe effects, i.e., extinction of one or two species; and (4) destructive effects, i.e., extinction of all species. The resulting effects data will contribute to an ecological risk assessment of the toxic agents compared with acute doses of ionizing radiation.

Nutrient-toxicant interactions in natural and constructed phytoplankton communities: results of experiments in semi-continuous and batch culture

Natural communities and clonal cultures of phytoplankton derived from large lakes in Yellowstone National Park (WY, USA) were employed to explore the effects of interactions between resource availability and toxic metals (divalent Cu and Cd) on pelagic plant communities. Results of semi-continuous competition experiments demonstrated strong direct and interactive effects of resource availability and additions of toxic metals (25-150 nmol l(-1)) in both natural and laboratory constructed four-species communities. Both endpoint community composition and population dynamics of individual species elicited responses to interaction between limiting resources and toxic metals. N limited growth in low-density batch cultures was suppressed by addition of Cu and these effects were specific to both algal species and level of available nitrate. Measures of semi-continuous culture effluent pH and pCu demonstrated that high levels of productivity can allow phytoplankton to selectively alter bulk water chemistry in the presence of elevated levels of metals to counteract their toxic effects. Concentrations of both limiting nutrients and toxicants employed were within the range of field-measured levels, suggesting that these types of interactions may be commonplace in natural environments. As such, environmental assessments considering potential impacts of toxic agents should take into account the nutrient status of the aquatic environment, and the interactions among stressors as demonstrated here.

Effects of long-term contamination of DDT on soil microflora with special reference to soil algae and algal transformation of DDT

DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) and its principle metabolites, DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) are widespread environmental contaminants but little information is available concerning their effects on non-target microflora (especially microalgae and cyanobacteria) and their activities in long-term contaminated soils. For this reason a long-term DDT-contaminated soil was screened for DDT residues and toxicity to microorganisms (bacteria, fungi, algae), microbial biomass and dehydrogenase activity. Also, five pure cultures isolated from various sites (two unicellular green algae and three dinitrogen-fixing cyanobacteria) were tested for their ability to metabolise DDT. Viable counts of bacteria and algae declined with increasing DDT contamination while fungal counts, microbial biomass and dehydrogenase activity increased in medium-level contaminated soil (27 mg DDT residues kg(-1) soil). All the tested parameters were greatly inhibited in high-level contaminated soil (34 mg DDT residues kg(-1) soil). Species composition of algae and cyanobacteria was altered in contaminated soils and sensitive species were eliminated in the medium and high contaminated soils suggesting that these organisms could be useful as bioindicators of pollution. Microbial biomass and dehydrogenase activity may not serve as good bioindicators of pollution since these parameters were potentially influenced by the increase in fungal (probably DDT resistant) counts. All the tested algal species metabolised DDT to DDE and DDD; however, transformation to DDD was more significant in the case of dinitrogen-fixing cyanobacteria.

Extrapolation methods for setting ecological standards for water quality: statistical and ecological concerns

: Extrapolation methods form the basis for most recent techniques used to set 'safe' levels of toxicants for ecosystems. Most methods use information from several single species toxicity tests to predict safety factors for protecting all species in all communities in a nation or group of nations. There are a number of statistical and ecological concerns with this approach. These include assumptions about the shape of the distribution of tolerance to a toxicant, the ability to extrapolate information on laboratory species and condition to field species and condition and to the condition of communities and ecosystems, and assumptions about the appropriateness of laboratory measures relative to ecosystem measures. The approach has not been validated for safety and, before the approach is fully applied, needs to be validated. Other methods can be used with the extrapolation approach to reduce uncertainties.

Screening for toxic effects on interspecies interactions: a mechanistic or an empirical approach?

The use of empirical and mechanistic approaches are possible in the development of tests to screen for a substance's potential to affect interspecies interactions. The advantages and disadvantages of the two approaches are discussed. An experimental study is presented, in which an empirical and a mechanistic screening test for effects on exploitative competition between bacterial species were established and perturbed with nalidixic acid. Comparison of test results indicates that the mechanistic test was faster, cheaper, more sensitive, and more quantitative. The empirical test attained similar sensitivity and quantification only if the dynamics of the competition event was continuously monitored; requiring even greater cost and time.

Polychlorinated Biphenyls: Transfer from Microparticulates to Marine Phytoplankton and the Effects on Photosynthesis

Polychlorinated biphenyls (PCB's) initially associated with microparticulates are incorporated into marine diatom cells. The time course of transfer is rapid; equilibrium is attained within several hours. Assays with chlorophyll a fluorescence in vivo indicate that the transferred PCB's reach sites in the photosynthetic machinery that are sensitive to the effects of these compounds.

Polychlorinated biphenyls may alter marine trophic pathways by reducing phytoplankton size and production

Polychlorinated biphenyls at concentrations of 1 to 10 micrograms per liter reduced phytoplankton biomass and size in natural estuarine phytoplankton communities grown within dialysis bags in situ in an estuarine marsh. In polychlorinated biphenyls-contaminated waters, these changes could increase the number of trophic levels and divert the flow of biomass from harvestable fish to jellyfish and other gelatinous predators.

Response to polychlorinated biphenyls of marine phytoplankton isolates cultured under natural conditions

Polychlorinated biphenyls (PCB) at a concentration of 10 mug/liter substantially but temporarily suppressed the growth rate and photosynthesis of two species of Thalassiosira recently isolated from Long Island Sound and grown in dialysis membrane bags suspended in the tidal channel of an estuarine marsh. Inhibition of carbon fixation was apparently due to reduced levels of chlorophyll a per PCB-treated cell, but no significant loss of function per unit of existing chlorophyll a was observed. Cell concentrations in all size classes (3.2- to 18.6-mum-equivalent spherical diameters) were markedly lower in PCB-treated cultures, with toal biomass equaling only 30% of that in control cultures throughout the experiment.

Chlorinated hydrocarbon pollutants and photosynthesis of marine phytoplankton: a reassessment

The chlorinated hydrocarbons DDT and PCB's (polychlorinated biphenyls), ubiquitous pollutants of the marine environment, have been observed to reduce the cell division rate of marine phytoplankton, thereby indirectly reducing the total photosynthetic carbon fixation in treated cultures. The photosynthetic capacity of each cell was not affected. Total marine photosynthesis will likely remain undiminished by these compounds, although alterations in phytoplankton communities through selective toxicity could effect herbivore populations.

Effects of PCB on interspecific competition in natural and gnotobiotic phytoplankton communities in continuous and batch cultures

The toxicity of polychlorinated biphenyls (PCB) to the diatomThalassiosira pseudonana (formerlyCyclotella nana), grown in pure and mixed cultures, was greatest when in competition with other species. Continuous cultures were superior to batch cultures for studying competitive interactions, and PCB caused greater alteration of species composition in continuous cultures than it did in batch cultures. Natural phytoplankton communities from Vineyard Sound, maintained in continuous culture, responded to PCB stress the same as did gnotobiotic communities, withT. pseudonana showing similar responses in both communities.A PCB concentration of 0.1 μg/liter (0.1 part per billion), a level not uncommon in natural waters, did not affect algal growth in pure cultures but caused substantial disruption of continuous culture communities. The possible impact of PCB pollution on natural phytoplankton communities is discussed.