Peter M. Chapman

Relative tolerances of selected aquatic oligochaetes to individual pollutants and environmental factors

Abstract Aquatic oligochaete distributions are a recognized indicator of environmental quality. The purpose of this study was to investigate the tolerances of 12 oligochaete species to specific pollutants and environmental factors and to relate tolerances to the use of oligochaetes as indicator species. Species were chosen for experimentation based on their present or potential importance as indicators of organic pollution. Acute toxicity data (96-h LC50 values) were obtained for 9 freshwater (Limnodrilus hoffmeisteri, Tubifex tubifex. Branchiura sowerbyi, Varichaeta pacifica, Quistadrilus multisetosus, Rhyacodrilus montana, Spirosperma nikolskyi, Spirosperma ferox and Stylodrilus heringianus) and 3 salt-water species (Monapylephorus cuticulatus, Tubicoides gabriellae and Limnodriloides verrucosus). The tolerances of these species were determined for 5 pollutants (cadmium, mercury, pentachlorophenol, pulp mill effluent and sewage sludge) and 4 environmental factors (pH, temperature, salinity and anoxia) both with and without sediment. Species considered to be eutrophic indicators were the most tolerant to sewage sludge, and oligotrophic species were the least tolerant. However, this was not true for pulp mill effluent or the chemical pollutants. The results confirmed the use of present oligochaete assemblages to indicate the degree of trophy in natural systems, but also suggested new assemblages for indicating the presence of particular chemical contaminants. The presence of sediments resulted in increased tolerances for all species, demonstrating the role of sediments as important modifiers of toxic effects on oligochaetes.

Relative tolerances of selected aquatic oligochaetes to combinations of pollutants and environmental factors

Abstract The field distributions of many species of aquatic oligochaetes have been interpreted as indicating their tolerance to pollution in general and organic pollution in particular, but these tolerances have not been tested in the laboratory. The purpose of this study was to investigate the tolerances of selected oligochaete species to combinations of pollutants and environmental factors. Species were chosen for experimentation based on the results of a previous study on the tolerance of oligochaetes to individual pollutants and environmental factors (Chapman et al., 1982). 96-h LC50 values were determined for 3 freshwater (Limnodrilus hoffmeisieri, Tubifex tubifex and Stylodrilus heringianus) and 2 salt-water species (Monopylephorus cuticulatus and Linnodriloides verrucosus) in relation to 4 pollutants (cadmium, mercury, pentachlorophenol and black liquor, a toxic component of pulp mill effluent). th different combinations of pH. temperature and salinity. Additional data were obtained for a 4th freshwater species: Quistadrilus (= Peloscolex) multisetosus. LC50 values were shown to depend on the environmental factors, but the relative tolerance rankings of most species to cadmium, pentachlorophenol and black liquor remained reasonably consistent throughout. Tolerance rankings for mercury were not consistent under varying environmental conditions.

Utility and relevance of aquatic oligochaetes in Ecological Risk Assessment

Ecological risk assessment (EcoRA) provides both a process and a framework to evaluate the potential for adverse ecological effects occurring as a result of exposure to contaminants or other stressors. EcoRA begins with problem formulation/hazard identification, progresses to effects and exposure assessment, and culminates with risk characterization (an estimate of the incidence and severity of any adverse effects likely to occur). Key components of EcoRA include determining: stressors/contaminants of concern; sensitive, exposed biota; and, appropriate tests and organisms for evaluating effects. Aquatic oligochaetes are not generally used directly in EcoRA because of three major perceptions. First, EcoRA personnel are generally not familiar with or comfortable using this group of organisms. Second, there is believed to be a paucity of widely accepted toxicity tests with these organisms. Third, their taxonomy is considered difficult and uncertain. In fact, aquatic oligochaetes potentially have great utility and relevance to EcoRAs because of factors including: their importance in the aquatic food chain (e.g. prey to fauna including fish and waterfowl; as a vector for contaminant movement through the food chain from bacteria); many species are widely distributed and well studied; representatives include fresh, estuarine and marine species; as a group, they range from sensitive to insensitive over a wide range of environmental insults; they have a long history of use in pollution monitoring and assessment; and, relevant toxicity and biaccumulation tests exist. Toxicity testing under defined conditions is appropriate for problem formulation while more realistic testing for effects assessment (e.g. microcosms) is logistically easier with this group of organisms than with others due to their relatively small size. The importance of aquatic oligochaetes for EcoRA, in particular of sediments, is particularly compelling.

Lethal and sublethal tolerances of aquatic oligochaetes with reference to their use as a biotic index of pollution

A series of recent studies have been completed by the authors involving: 1) determining the lethal tolerances of 12 oligochaete species classified (from ecological studies) as tolerant, moderately tolerant and intolerant to selected chemical toxicants and environmental factors under defined bioassay conditions with and without sediment; 2) determining lethal tolerances of candidate species to toxicants in combination with a range of abiotic factors; 3) measuring respiratory stress imposed by exposure to individual and combined sublethal concentrations of toxicants and environmental factors; and, 4) determining differences in lethal tolerance and respiratory stress between individual and mixed species. Surprisingly few previous studies have been done in this area considering the importance of oligochaetes as field pollution indicators. The results of the above major studies coupled with histopathological work are reviewed. Data from these studies substantiate the present use of oligochaete species assemblages as indicators of organic pollution and suggest their use in the laboratory for toxicant screening tests. The range of responses of different oligochaete species to individual and combined stress is complex, particularly in mixed species, which provides useful indications of specific stress factors. The application of these experimental laboratory studies to field situations is described.

Hair today, gone tomorrow: induced chaetal changes in tubificid oligochaetes

Laboratory experiments were conducted to determine the extent of chaetal variation in the tubificids Tubifex tubifex and Ilyodrilus frantzi and the naidids Specaria fraseri and Nais communis under varying environmental conditions. Univariate exposures were carried out using different levels of pH, salinity, water hardness and mercury. We were not able to induce chaetal changes in the two naidids tested. However, we were able to reduce the hairs and pectinations of T. tubifex with exposure to pH, salinity and to hard water such that the bergi form was produced. Prolonged exposure to low or high pH resulted in the total loss of hairs and pectinates such that the blanchardi form was produced. We were able to eliminate the hairs and pectinates of I. frantzi (capillatus) in soft, freshwater exposures such that the bifidus form of I. frantzi was produced. Conversely, in hard or saline water we were able to induce formation of hairs and pectinates on the bifidus form such that the capillatus form was produced. These changes occurred at time intervals ranging from a few days to two months.

Seasonal changes in interstitial salinities and seasonal movements of subtidal benthic invertebrates in the Fraser River estuary, B.C.

The subtidal benthic fauna of the lower Fraser River, a salt-wedge estuary, was sampled monthly from June 1977 to August 1978 in mud substrates at six stations ranging from oligohaline to polyhaline. Subtidal interstitial salinities were also measured and were related to the seasonal distribution of the estuarine benthic fauna. Interstitial salinities of silty sediments do not vary diurnally, but the transition zone between salt and fresh interstitial water is cyclically shifted up- and downstream in relation to freshwater discharge, leading to seasonal shifts in the distribution of benthic infaunal species. Seasonal shifts are shown to occur in the oligochaetes Limnodrilus hoffmeisteri, Tubifex tubifex, Tubificoides gabriellae, Paranais litoralis, Specaria fraseri, Nais communis and Nais elinguis, and of the polychaetes Eteone longa, Amphicteis sp. and Polydora kempi japonica. These species comprised over 25% of the total taxa collected and over 60% of the individuals collected. The data on other species distributions do not conflict with the hypothesis of cyclic changes related to seasonal interstitial salinities. The changes vary in extent in relation to runoff, and appear to be a feature of salt-wedge estuaries in general.

Effects of species interactions on the survival and respiration of Limnodrilus hoffmeisteri and Tubifex tubifex (Oligochaeta, tubificidae) exposed to various pollutants and environmental factors

Abstract Laboratory tests were conducted to determine short-term (96 h LC 50) and physiological (respiration) effects of various pollutants (Cd, Hg, NaPCP) and environmental factors (temperature, pH, salinity, anoxia) on mixtures of two freshwater oligochaete species: Limnodrilus hoffmeisteri and Tubifex tubifex . Comparisons with similar data for individual species indicated that mixed species were significantly more tolerant of toxicants, similarly tolerant of environmental factors and less tolerant of anoxia. Although individually these species regulated respiration rate, in mixed culture they were non-regulators and respiratory changes in response to stress appeared to vary depending on test conditions.

Measurements of the short-term stability of interstitial salinities in subtidal estuarine sediments

Diurnal comparisons of sediment interstitial salinities with those of the immediately overlying water were conducted subtidally at five stations in the Fraser River estuary, B.C. These in situ studies indicated that the interstitial salinities of sediments containing a high proportion of silt were relatively constant despite large fluctuations in water column salinities; however, in sands, interstitial salinities closely followed diurnal salinity variations in the water column. Laboratory penetration studies were conducted using relatively undisturbed natural sediments. The results of the in situ and laboratory studies indicated that exchange between the interstitial and overlying water was influenced by three major factors: the rate of water flow above the sediment, the relative salinities of the interstitial and overlying water and the sediment composition.

Salinity Tolerance in Some Selected Aquatic Oligochaetes

Salt tolerance of the freshwater tubificid Limnodrilus hoffmeisteri varied from an LD 50 of 10 ppt to 10.5 ppt for mature and immature worms without sediment, 9.4 to 10.5 in sand, and 14.3 for immatures acclimated to 5 ppt. Ilyodrilus templetoni was similarly intolerant to higher salinities. The estuarine Tubificoides gabriellae tolerated salt water, but was susceptible to freshwater, with LD 50s of 2 and 3.5 when acclimated to 5 and 10 ppt sea water. It survived immersion in freshwater for 3 hours. The estuarine naidids Paranais litoralis and frici experienced mortalities at both high and low salinities but showed a wide tolerance range. The coastal tubificid Monopylephorus irroratus showed almost complete tolerance to the salinity range employed. The findings reflected field distributions especially when interstitial salinities were measured, but worms did not occupy the full range of habitats possible in terms of salinity alone.

Oligochaete respiration as a measure of sediment toxicity in Puget Sound, Washington

Respiration rate measurements were conducted with the marine oligochaete Monopylephorus cuticulatus Baker and Brinkhurst to determine the sublethal toxicity of sediments collected from Puget Sound, Washington. Worms were exposed to elutriates prepared from centrifuged sediment slurries. Standard respiration rates were measured at high dissolved oxygen levels for each sample tested and were compared with control and other test results. A total of 97 sediment samples were tested; 40 samples demonstrated significant respiration effects (elevation or depression). Comparison with results of other tests conducted at the same stations or geographic locations (genotoxicity to fish cells, lethality to sensitive species, reproductive impairment tests) indicated very good agreement on broad scale toxicity patterns at different geographical areas, and that respiration measurements effectively determined sublethal toxicity of sediments. This study represents the first application of respiration measurements as a sublethal toxicity test for field-collected sediments.