David Pascoe

Chronic toxicity of cadmium toChironomus riparius Meigen — effects upon larval development and adult emergence

Chronic cadmium toxicity tests were carried out withChironomus riparius Meigen using a static-with-replacement exposure procedure. Significant reductions in larval development, survival and production were detected at 0.15 mg Cd l−1 a value approximately 5000 times lower than the 48 h LC50 for fourth instar larvae. The first instar appears to be the most critical stage in terms of sensitivity, with the number of adults eventually emerging reflecting first instar mortality. Male emergence was slightly delayed at 0.15 mg Cd l−1. The results of this study illustrate the importance of chronic toxicity tests in identifying sensitive life cycle stages and explaining pollutant-induced stress.

Heavy metal toxicity to fish and the influence of water hardness

Toxicity tests with rainbow trout confirm that cadmium is less toxic in hard water (96 hr LC50=2.6 mg Cd/L) than in soft water (96 hr LC50=1.3 mg Cd/L). Water quality studies indicate that this is not due to a chemical reduction of available cadmium in hard water and no significant differences in cadmium uptake were detected between fish from the two levels of hardness. Possible explanations for the effect of hardness on heavy metal toxicity to fish are discussed.

Toxicity of four common pollutants to the freshwater macroinvertebratesChironomus riparius Meigen (Insecta:Diptera) andGammarus pulex (L.) (Crustacea:Amphipoda)

The lethal toxicities of the four pollutants 3,4-dichloroaniline (DCA), atrazine, copper, and lindane were determined for the 2nd larval instar of the insectChironomus riparius Meigen and the juvenile stage (2nd or 3rd moult) of the crustaceanGammarus pulex (L.). Median lethal concentrations (LC50s) were determined over a 240 h test period. The order of toxicity of the test chemicals is different for each species. ForC. riparius, lindane was the most toxic, followed by copper, DCA, and atrazine. During the first 96 h of exposure, the order forG. pulex was copper, lindane, then DCA and atrazine with similar LC50 values. However, at 240 h lindane replaced copper as the most toxic chemical toG. pulex. The relative sensitivity of the two species was dependent on both the toxicant and the exposure period. The lethal concentrations determined for the four chemicals are compared to the results of other toxicity studies and discussed with respect to current standard test methods.

Episodic pollution--a comparison of brief and continuous exposure of rainbow trout to cadmium.

The toxicity of cadmium to rainbow trout fry resulting from brief or continuous exposure is compared. Results of tests involving brief cadmium exposure followed by restoration to clean water indicate that postexposure mortalities may result from contact for as little as 32 min to 1.0 mg Cd liter-1 or 10 min to 10 mg Cd liter-1. These results highlight the inadequacy of standard toxicity tests in predicting the consequences of an episodic pollution incident such as that resulting perhaps from an accidental spillage. For example, the median lethal time (LT50) following continuous exposure to 1.0 mg Cd liter-1 is 1900 min whereas exposure for only 32 min will ultimately result in 50% mortality. The term median postexposure lethal time (peLT50) is proposed as a means of assessing and comparing the results of brief exposure to a pollutant and it is suggested that brief or episodic exposure tests should be incorporated into the hazard evaluation process.

Lethal and sub-lethal toxicity of field simulated farm waste episodes to several freshwater invertebrate species

Abstract Four field experiments designed to simulate the effects of the individual components of farm waste effluent (increased ammonia, reduced dissolved oxygen concentrations) on the invertebrate fauna of receiving waters were carried out on two second order streams in South Wales. In two studies the dissolved oxygen concentration was reduced to 2 and 1 mg 1−1 by the oxidation of sodium sulphite, and in a further two studies ammonia concentrations were raised to 5 and 7 mg 1−1 by dosing with ammonium chloride and the toxicant maintained in the unionized state by the simultaneous addition of sodium hydroxide to raise pH to approx. pH 9. During each simulation (6–24 h in duration) the response of several invertebrate species placed in the downstream treatment zone(s) was compared with that of animals maintained in an upstream untreated reference zone. Significant invertebrate mortalities were recorded only under conditions of reduced dissolved oxygen. The feeding rate of Gammarus pulex was significantly reduced during dosing with ammonia but recovered post-exposure. Parasitism of G. pulex with Pomphorhynchus laevis resulted in a reduced feeding rate and an increased mortality in comparison to uninfected animals. The disruption of precopula in G. pulex was a sensitive and rapid indicator of stress under both reduced dissolved oxygen and increased ammonia concentrations.

The bioconcentration of zinc by Gammarus pulex (L.) and the application of a kinetic model to determine bioconcentration factors

Abstract The bioconcentration, and subsequent elimination, of zinc by the freshwater amphipod Gammarus pulex (L.) were determined experimentally in the laboratory at five zinc exposure concentrations (0.41–2.02 mg/l). A first-order kinetic model, modified for naturally occurring trace chemicals, was then used to calculate uptake ( K 1 ) and elimination ( K 2 ) rate constants from which the bioconcentration factors (BCF) could be predicted. Good agreement was found between the recorded and predicted BCFs and it is suggested that the model could have wider use for the study of substances naturally present at trace levels within animal tissues.

Short-term experimental acidification of a Welsh stream: toxicity of different forms of aluminium at low pH to fish and invertebrates

A 24-hr dosing experiment was carried out in a soft-water stream in upland Wales during which four separate zones were created by the simultaneous addition of sulphuric acid, aluminium sulphate, and citric acid. An upstream control zone (A), an acid zone pH 4.9 (B), an aluminium and acid (total filterable aluminium 0.27 mg/L, pH 4.9) zone (C) and a downstream zone (D) of aluminium complexed with citrate at low pH (total filterable aluminium 0.23 mg/L, pH 4.9). Test species exposed in all zones were the invertebratesGammarus pulex (L.),Baetis rhodani (Pict.),Ephemerella ignita (Poda) and the fishSalmo salar L.,Salmo trutta L. andCottus gobio L.Response criteria measured were mortality, feeding, effects of pretreatment, brief-exposure, and the ability of animals to recover. Minimal effects were observed in the control and acid zones whilst large mortalities and reduced feeding were recorded in the acid and aluminium zone. These effects were significantly reduced in the acid, aluminium and citrate zone due to complexation of aluminium with citrate.

The acute and chronic toxicity of cadmium to different life history stages of the freshwater crustaceanAsellus aquaticus (L)

Different life-history stages of the freshwater isopod crustaceanAsellus aquaticus were exposed to a range of cadmium concentrations using a semi-static toxicity testing procedure. Median lethal concentrations (96-hr LC50) ranged from 80 Μg Cd/L for juveniles to >2,000 Μg Cd/L for embryos. Pre-treatment of eggs with cadmium did not increase their tolerance to the metal as juveniles. The responses of each stage are discussed in relation to the use of macroinvertebrate toxicity test data in predicting the hazardous effects of pollutants.

Effects of acid, aluminium and lime additions on fish and invertebrates in a chronically acidic welsh stream

A chronically acidic stream, mean pH 5.2, in upland mid-Wales was subjected to an induced episode of acidity, during which acid, Al and limestone were added at different points along the stream length. An upstream reference zone (A), an acid zone (B), an acid plus Al zone (C) and a downstream zone of Al at low pH with added limestone to increase pH (D) were created for a 24 hr period. Four species of fish and 10 species of invertebrates were exposed in each zone and response criteria measured included mortality, metal uptake, feeding and the ability of stressed animals to recover. Fish mortalities were greater in zones B and C than in zone A and were greatly reduced by the addition of lime in zone D. Overall mortality was low amongst the invertebrate species found in acid waters. Greatest mortalities were recorded for Gammarus pulex. G. pulex infected with the acanthocephalan parasite Pomphorhynchus laevis exhibited greater mortality than uninfected animals. The feeding rate of G. pulex was suppressed in all zones during the dosing period; uninfected G. pulex consumed more than infected animals, and the feeding rate of all gammarids increased post-dosing but not to the level of unexposed animals. Aluminium concentrations in fish gills increased with time. Invertebrate body burdens of Al were greatest in zone D, with significant increases over the dosing period for both G. pulex and Isoperla grammatica. No significant patterns were observed in the concentration of Ca, Na or K for either fish or invertebrates.

Laboratory and field evaluation of a behavioural bioassay—The Gammarus pulex (L.) precopula separation (GaPPS) test

Abstract A bioassay, based upon the reproductive behaviour of the amphipod Gammarus pulex , was evaluated for its application in detecting freshwater pollutants. In the laboratory the bioassay proved to be useful in rapidly detecting a wide range of pollutants at concentrations significantly below those causing acute lethal toxicity and in the field it responded rapidly to a variety of pollutant inputs. The results indicate that this bioassay is simple, cost-effective and reliable and could be employed effectively for detecting and quantifying pollutants.