K. Simkiss

Evidence of differences in the biotransformation of organic contaminants in three species of freshwater invertebrates

Acute static bioassays were performed using three freshwater invertebrate species (the oligochaete Lumbriculus variegatus, the fingernail clam Sphaerium corneum and the larvae Chironomus riparius) exposed separately to a variety of 14C radiolabelled contaminants. The aim of this work was to investigate if the chemicals remained as parent compounds after the treatments. Chemicals used were 2,4-dichlorophenol; 2,4,5-trichlorophenol; pentachlorophenol; pyrene; Fenpropidin, and Trifluralin. Homogenates of the whole body tissue of each organism were prepared and total radioactivity was measured. Contaminants were then extracted into organic solvents and analysed by high-pressure liquid chromatography techniques. Chromatograms showed that most of the substances extracted were present as parent compounds in S. corneum and in L. variegatus. In contrast, for C. riparius a low proportion of the chemicals was recovered as parent compounds. These results suggest that different metabolic processes could take place in the different species.

An X-Ray Absorption Spectroscopy Study of the Structure and Transformation of Amorphous Calcium Carbonate from Plant Cystoliths

Cystoliths are intracellular calcified bodies which are found in great numbers in the leaves of many higher plants such as Ficus retusa. The mineral part of these deposits is amorphous calcium carbonate, which transforms to calcite only when moistened. We have followed this transformation by using X-ray spectroscopy by measuring the local atomic structure around the calcium of the isolated dry cystoliths and after moistening them with water. The production and maintenance of the amorphous phase is clearly under biological control. The cystoliths may act as a pH-stat which neutralizes hydroxide ions. Potentially cytotoxic cations also accumulate in the cystoliths. Rapid precipitation of calcium carbonate into the organic matrix could favour the amorphous phase, which may be maintained by low concentrations of magnesium and phosphate, which are inhibitors of the nucleation of crystalline phases.

Pyrene bioavailability; effect of sediment-chemical contact time on routes of uptake in an oligochaete worm.

Bioavailability of sediment-sorbed compounds may vary with increasing contact time. This may result in the dietary uptake route becoming more significant as conditions in the gut flora aid the extraction of contaminants, which have migrated into sites within the sediment particle. Such mechanisms may have important implications on risk assessments performed on substances released into the environment. A series of experiments were carried out using sediment spiked with 14C-labelled pyrene, a polycyclic aromatic hydrocarbon. The sediment was left at room temperature over a period of 220 days. Periodically (at 0, 1, 14, 28, 70, 220 days) the sediment was used to perform a bioaccumulation study using the freshwater oligochaete Lumbriculus variegatus. A novel methodology using feeding and (decapitated) non-feeding worms, allowed differentiation between uptake via ingestion and simple sorption. Results showed that there was a decline in bioavailability with time and that this was a 3 stage process. A rapid initial decline was observed over the first day when a 40% decrease was measured, an intermediate period were levels remained stable (day 14 to day 70) and an ultimate decrease in pyrene activity in worm tissue of 70% after 220 days. Over this period the chemical extractability of pyrene also decreased by 50%, as the chemical migrated deeper into unavailable sites within the sediment matrix. Normalising bioavailability to the chemically extractable fraction of pyrene within the sediment provided an overall decrease in bioavailability of 58%. The importance of the dietary route of uptake for pyrene varied during the sediment aging process, reflecting the changes in the physico-chemical interactions between the pyrene, sediment and pore water.

Can adsorption isotherms predict sediment bioavailability

The adsorption and desorption of 2,4-dichlorophenol (DCP) and pentachlorophenol (PCP) were studied for a range of synthetic particles, a dimethylditallowammonium exchanged clay and a natural sediment. The synthetic particles were Dowex 1X8400, Toyopearl Phenyl 650M and Toyopearl SP 650M. The bioaccumulation of the DCP and PCP from these particles was then studied using the oligochaete, Lumbriculus variegatus. There is a correlation between contaminant-particle interactions, as determined from adsorption and desorption isotherms, and bioaccumulation. Bioaccumulation by L. variegatus was found to be highest from the systems where differences in the classification of adsorption and desorption isotherms were observed.

A simple larval diet for population studies on the blowfly Lucilia sericata (Diptera: Calliphoridae)

Abstract. 1 A simple artificial diet was devised for larvae of Lucilia sericata Meigen. 2 A basic diet of 20 g/1 agar with 20% horse blood and added yeast sustained normal growth and development, as compared with a lamb meat control. 3 When yeast was added to the blood agar diet at 50 gp>1, both peak and final larval weights were increased by 25–50% at higher larval densities (2–8 larvae/g diet) and the hatchling‐adult development period was reduced by about 3 days. 4 No adult insects emerged on an agar‐yeast diet without blood. Increasing the concentration of blood from 10% to 20% increased adult weight at emergence by 50%, though developmental period was not significantly affected. 5 Increasing larval density significantly reduced the weights of pupae and emergent adults (by up to 50%), both on the blood‐agar‐yeast diet and the lamb meat control. Percentage survival fell from 80–90% to below 10% on the blood‐agar‐yeast diet at the highest densities of 4 or 8 larvae/g diet, though survival on lamb was not significantly affected by density.

Metal ion metabolism in the moulting crayfish (Austropotamobius pallipes)

Abstract 1. 1. The hepatopancreas, antennal gland, gills, gonads. muscle, stomach, carapace, gastroliths and blood of 52 crayfish (Austropotamobius pallipes) have been analysed for copper, zinc, iron, manganese and calcium throughout the moult cycle. 2. 2. There are significant changes in most of these metals at the time of ecdysis. 3. 3. The results are interpreted in terms of sites of metal storage and mobilization in the hepatopancreas and evidence is presented to suggest that copper and zinc are metabolized along related but independent pathways.

Effects of population density and cadmium toxicity on growth and survival of blowflies.

The blowfly Lucilia sericata has been reared on artificial diets containing from 0 to 200 mg Cd kg(-1) at population densities ranging from 8 larvae per 4-g diet to 8 larvae per 32-g diet. Peak larval weight, development period, pupal weight, adult-emergence weight, and fecundity were measured. Larvae of blowflies respond to food deprivation by a reduction in larval weight and subsequent pupal and adult size. Contaminating the food supply with cadmium produced similar additive effects, reduced the growth rate, and increased the age of pupation. The results are of importance in determining the effects of environmental pollutants on population dynamics.

The influence of gut microorganisms on zinc uptake in Helix aspersa

An artificial diet was prepared that enabled the snail Helix aspersa to be fed food containing varying amounts of metals, antibiotics or bacteria. By this means it is possible to show that the body burden of zinc was significantly correlated with the dietary intake. The snail was, however, able to detect high concentrations of the metal and reduced its intake of such contaminated food. The bacterial population of the alimentary tract modified the amount of zinc absorbed from the diet. It appears, therefore, that biological monitoring programmes, based upon bioaccumulation measurements, should take these influences into account.

Biocide testing using particles with controlled surface properties (artificial sediments)

Sediments may play an important role in the accumulation of contaminants by benthic organisms. This work uses artificial particles to model natural systems and to provide a way of predicting bioavailability from sediment/contaminant interactions. The artificial particles used were a range of high performance liquid chromatography resins and a dimethylditallow ammoniumexchanged clay. The bioavailability of 2,4-dichlorophenol on these particles to the midge larva Chironomus riparius was compared with that from sand and a natural sediment. The experiments were designed so that water uptake and accumulation due to the ingestion of particles could be distinguished. The results show that very strong or very weak electrostatic interactions of the contaminant with the particles results in little accumulation of the contaminant via ingestion. When the contaminant is weakly bound to the particles by van der Waals forces, the contaminant can be released from the ingested particles. In these experiments, this occurred when the contaminant–particle interaction was hydrophobic, and it is under these conditions that 2,4-dichlorophenol was most bioavailable.

The influence of particle surface characteristics on pollutant metal uptake by cells.

The phosphatic mineral, hydroxyapatite, and two ion exchange resins have been used as artificial sediment particles. The surface properties of these materials have been studied using the Langmuir adsorption isotherm to calculate the binding capacity (B(max)) and the adsorption constant (K(L)) for zinc and cadmium ions. Mussels (Mytilus edulis) were fed on the particles and their digestive glands were subsequently removed and subjected to cell fractionation. The supernatant fraction was used to determine cytosol metal levels as a measure of the materials absorbed from the ingested particles. The level of cytosol zinc and cadmium was correlated with the K(L) values of the artificial sediments. It is suggested that phagocytosis of sediment particles plays an important part in transferring pollutants into benthic organisms and that the efficiency of this process is related to the adsorption coefficient of the particle surfaces.