Sediment Toxicity Assessment: Comparison of Standard and New Testing Designs

Standard methods of sediment toxicity testing are fairly well accepted; however, as with all else, evolution of these methods is inevitable. We compared a standard ASTM 10-day amphipod toxicity testing method with smaller, 48- and 96-h test methods using very toxic and reference sediments. In addition we compared parallel exposures of single species, either the amphipod Ampelisca abdita or the mysid Americamysis bahia, to multiple species, mysid, and amphipod, cohabiting the same types of chambers. These comparisons were performed for both water-only and sediment-water tests. Results of the comparison of the standard ASTM 10-day amphipod test with the smaller, 48- and 96-h test chambers indicate that survival was high in both test designs using the reference sediment. With toxic sediments, complete mortality occurred in less than 48 h using the smaller experimental chambers and only after 96 h in the larger experimental chambers. We concluded that although time to death is shorter in the smaller, shorter exposure chambers, there was no overall change in mortality for the organisms, and that the smaller chambers were predictive of the results obtained with larger chambers and longer exposures. For multiple species testing in whole sediment exposures there was no change in toxicity to either the amphipod or the mysid when they cohabited the same chamber. In contrast, for water-only exposures, A. bahia demonstrated less sensitivity when cohabiting the same chamber as A. abdita. Therefore, during whole sediment testing we can add A. bahia and A. abdita to the same test chamber without changing the toxicity to either species; however, in our 10-ml water-only exposures, the species should be tested separately. Received: 16 November 1999/Accepted: 13 May 2000     

Feeding problems in young PKU children

Behavioural feeding problems were found to be more prevalent in a group of 15 PKU children aged 1-5 years when compared to non-PKU controls. The parents of PKU children identified poorer appetites ( p < 0.01), a more limited range of foods consumed ( p < 0.03) and more gastrointestinal symptoms such as vomiting and constipation ( p < 0.03) than control children. The children were slower to feed ( p < 0.03), were more likely to dislike sweet foods and some ate separately from the rest of the family at mealtime ( p < 0.03). The effects on normal feeding behaviour should be considered when advocating strict diet therapy for young PKU children.     

Biotic Factors Modifying Acute Toxicity of Aqueous Cadmium to Estuarine Amphipod Leptocheirus plumulosus

A 96-h exposure to aqueous cadmium (Cd) is the recommended reference toxicity test for 10-day sediment bioassays with the estuarine amphipod, Leptocheirus plumulosus (US EPA 1994). This water-only test was used to assess the influence of organism size, sex, and nutritional status on the sensitivity of laboratory-cultured L. plumulosus to Cd. In addition, the response of field-collected amphipods was compared to similarly sized laboratory animals to assess potential seasonal changes in Cd sensitivity. Lipid content of test organisms was measured in these seasonal experiments and those evaluating effects of nutritional status because of its potential as an indicator of physiological condition. LC₅₀ values of laboratory animals size-sorted on nested 500-, 710-, and 1000-μm mesh sieves, increased with size class: 0.36, 0.65, and 0.88 mg Cd/L, respectively. Gravid females were less sensitive than males or mature females to aqueous Cd. Studies on the influence of the molt cycle on Cd toxicity indicated enhanced sensitivity of immediate postmolt animals that may explain some of the observed differences in Cd tolerance. Nutritional effects were investigated by comparing the sensitivity of fed and starved laboratory-reared amphipods. Starved juveniles and adults were significantly smaller than their fed counterparts and exhibited a 28–43% reduction in lipid content, respectively. However, comparison of LC₅₀ values indicated no significant differences in sensitivity to Cd between starved and fed juveniles (0.23 vs 0.30 mg Cd/L) or adults (0.37 vs 0.52 mg Cd/L). Field-collected amphipods were typically more sensitive to Cd than laboratory animals, regardless of the season, although their lipid content varied, ranging from 6.6% in August to 13.7% in November. Results are discussed with respect to the use and interpretation of toxicity tests with this species. Received: 18 February 1997/Accepted: 5 May 1997     

The Synthesis of Sulphated Mucopolysaccharide in Mouse Liver Following Carbon Tetrachloride Injury: I. Autoradiographic Studies

Autoradiography of mouse liver after the administration of ³⁵S-sodium sulphate shows transient concentration of the isotope in sinusoidal walls. This phenomenon is markedly exaggerated in the acute stages of carbon tetrachloride (CCl₄) poisoning with radioactivity appearing over viable sinusoidal cells and extracellular necrotic spaces. This is maintained for several days and there is condensation of the isotope over prominent reticulin fibres in the centrilobular zones during the stage of recovery. Negative results are obtained if the sinusoidal cells are included in the necrotic process as induced by CCl₄ or by the local application of cold to the surface of the liver. It is concluded that liver sinusoidal cells have a capacity for mucopolysaccharide synthesis which is exaggerated following the induction of hepatocyte injury. There is also evidence for continuing synthesis of sulphated mucopolysaccharide in the cirrhotic liver in relation to fibrous trabeculae and hepatocyte degeneration.     

Media Exchange Method for Demonstrating Killing of L-Phase Variants in Solid Media by Normal Human Serum

Normal human serum has been shown to kill L-phase variants in a fluid system by the action of antibody plus complement. Previous studies, however, failed to demonstrate such killing in solid media. This failure probably resulted from inhibition of complement by medium components such as agar and NaCl. A method was developed which circumvents the problems of the anticomplementary properties of agar media and the requirement of some L-phase variants for concentrations of salt that inhibit complement. Using this method, we have demonstrated in solid media the killing by normal human serum of the L-phase variants of Staphylococcus aureus, Proteus mirabilis, Streptococcus pyogenes, S. faecalis, Pseudomonas aeruginosa, and Salmonella typhi. This method provides a relatively simple and graphic means for studying host humoral factors lethal for L-phase variants.