Marina G. Taylor

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.

Bone mineral : evidence for hydroxy groups by inelastic neutron scattering

Inelastic neutron scattering (INS) spectroscopy which is especially sensitive to vibrations of groups with hydrogen has been used to resolve the extent of substitutions at the hydroxy group site in bone. Bone is a complex material consisting of a mineral apatite (Ca5(PO4)3 OH), in an extracellular protein matrix. Many aspects concerning the composition of the mineral are controversial. It has been suggested that there is complete substitution by carbonate at the hydroxy site. Bands assigned to hydroxy vibrations are often not resolved in the infrared and Raman spectra. We show, by INS, that in ox femur bone 40–50% of the hydroxy groups are not substituted. The inelastic neutron scattering experiment opens up new opportunities to monitor changes in bone composition which are important in bone ageing and some pathological conditions.

Hydrated sites in biogenic amorphous calcium phosphates: An infrared, Raman, and inelastic neutron scattering study

Amorphous minerals are widely distributed in biology, and occur as carbonates, phosphates, and silica. Calcium and magnesium are the major cations in the phosphate deposits, but in addition, there is usually an organic component, and the minerals are hydrated with up to 20% water. Such deposits are found as intracellular granules in a variety of invertebrates such as the shore crab Carcinus maenas. These intracellular granules and synthetic amorphous calcium phosphates and crystalline apatite have been studied by infrared, Raman, and inelastic neutron scattering to establish the protonation of the phosphates and the structure of the water in these deposits. Monetite and newberyite were used as model compounds for comparison. It is concluded that the water occurs in regions that are only loosely associated with the cations in these solids.

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.

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.

Corrosion of Intracellular Granules and Cell Death

The snail Helix aspersa has large numbers of calcium cells in its hepatopancreas which contain membrane-bound intracellular granules of CaMgP2O7. These inorganic deposits are the sites of accumulation of a wide variety of cations and act as a detoxification mechanism that traps a number of dietary metals once they have entered the animal. This study concentrates on the mechanism of incorporation of manganese ions into these deposits by using electron microscopy, ultra-low-angle X-ray scattering and extended X-ray absorption spectroscopy. The results show that manganese ions cause a localized corrosion of these intracellular granules with a consequent release of calcium ions. This release appears to overwhelm the calcium-regulatory mechanisms of these cells and leads to their death and subsequent shedding into the lumen of the alimentary tract. The concept of intracellular corrosion is a novel interpretation of a previously unsuspected biochemical lesion.

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.

Metal toxicity in two rodent species and redox potential: Evaluation of quantitative structure-activity relationships

A quantitative structure-activity relationship study of acute toxicity in the mouse and rat is described for the soluble salts of a relatively large number of metals (between 25 and 30 in total). Electrode potential is the major determinant of acute metal toxicity (R = 0.85 and 0.86) for an intraperitoneal dose in the mouse, whereas the addition of ionic radius and polarizability enables the inclusion of notable outliers in the original expression, such as beryllium and barium, thus giving a good correlation (R = 0.87) with toxicity for 27 metal compounds. These findings are rationalized on the basis of relative ease of ionization, electron affinity, and transport factors of the metals and their ions, thus being consistent with the hard and soft acids and bases properties of metals and their biological reactivities.