B. Thomas Johnson

Environmental and chemical factors influencing the biodegradation of phthalic acid esters in freshwater sediments

Abstract A wide range of environmental and chemical factors influenced the biodegradation of simple and complex phthalic acid esters in an aquatic environment. The length and configuration of the alkyl phthalate diester significantly affected the primary biodegradation of di-n-butyl (DBP), di-2-ethylhexyl (DEHP), di-isooctyl (DIOP), and di-isononyl (DNIP) phthalate. After 14 days incubation in aerobic sediments at 22°C, less than 2% of the branched-chain alkyl phthalates—DEHP, DIOP and DINP (at μg concentrations)—were biodegraded, compared with 85% of the linear alkyl DBP. Primary biodegradation of DEHP, DIOP and DINP was significantly greater at high concentrations (> μ g litre −1 ) and high temperatures (> 22°C) in freshwater sediments. Pre-exposure of the sediments to DBP, DEHP, DIOP and DINP did not influence their biodegradation. The addition of organic nutrients significantly affected the primary biodegradation of DBP with varied results, depending on the nutrient, its concentration, and the time of addition. Neither inorganic nitrogen nor phosphorus alone or in combination influenced the degradation of DBP. The complex alkyl phthalate DEHP in sediments biodegraded under anaerobic conditions; even though the process was slow, both primary and ultimate degradation did occur.

Toxicological and chemical screening of Antarctica sediments: Use of whole sediment toxicity tests, microtox, mutatox and semipermeable membrane devices (SPMDs)

Abstract Eight whole sediment samples from Antarctica (four from Winter Quarters Bay and four from McMurdo Sound) were toxicologically and chemically evaluated. Also, the influence of ultraviolet radiation on the toxicity and bioavailability of contaminants associated with the sediment samples was assessed. The evaluations were accomplished by use of a 10-day whole sediment test with Leptocheirus plumulosus, Microtox®, Mutatox® and semipermeable membrane devices (SPMDs). Winter Quarters Bay sediments contained about 250 ng g−1 (dry weight) total PCBs and 20 μg g−1 total PAHs. These sediments elicited toxicity in the Microtox test and avoidance and inhibited burrowing in the L. plumulosus test. The McMurdo Sound sediment samples contained only trace amounts of PCBs and no PAHs, and were less toxic in both the L. plumulosus and Microtox tests compared to the Winter Quarters Bay sediments. The sediments from McMurdo Sound apparently contained some unidentified substance which was photolytically modified to a more toxic form. The photolytic modification of sediment-associated contaminants, coupled with the polar ozone hole and increased incidence of ultraviolet radiation could significantly increase hazards to Antarctic marine life.

Biological effects of Kepone and mirex in freshwater invertebrates

Acute and chronic toxicity studies of Kepone® (chlordecone) and mirex were conducted with daphnids (Daphnia magna), amphipods (Gammarus pseudolimnaeus), and larvae of a midge (Chironomus plumosus). Acute toxicities of Kepone ranged from a 48-hr EC50 of 350μg/L for midges to a 96-hr LC50 of 180μg/L for amphipods, whereas the acute toxicities of mirex to all three taxa exceeded 1000μg/L. Maximum acceptable toxicant concentrations (MATCs) for Kepone and mirex were estimated by measuring reproduction of daphnids, growth of amphipods, emergence of midges, and survival of all organisms. MATC for Kepone was estimated to be between 9 and 18μg/L for daphnids, between 1 and 2μg/L for amphipods, and between 8.4 and 18μg/L for midges; MATC for mirex exceeded 34μg/L for daphnids and midges, but less than 2.4μg/L for amphipods. The concentration of Kepone and mirex accumulated by daphnids was 760 and 8025 times, respectively, the concentration in water. Estimated times for elimination of 50% of the residues by daphnids were 141 hr for Kepone and 12 hr for mirex.

Collection and detection of lipophilic chemical contaminants in water, sediment, soil, and air—SPMD-TOX

This toxicological screening tool is a method designed to collect and detect the presence of toxic lipophilic chemical contaminants in water, sediment, soil, and air. This method is applicable to the following types of samples: (1) surface water, groundwater or wastewater; (2) sediment or pore water; (3) soil; and (4) air. A pasive sorptive tool, known as the semipermeable membrane device (SPMD), collects lipophilic chemical contaminants from water, sediment, soil, and air and a short-term, microscale in vitro procaryotic assay known as the Microtox acute basic test assay (Microtox®, Azur Environmental, Carlsbad, CA), detect accumulated toxins.

Xenobiotic Perturbation of Microbial Growth as Measured by CO2 Uptake in Aquatic Heterotrophic Bacteria

Abstract A microbiological assay, based on the Wood and Werkman reaction (i.e., dark reaction carboxylation by heterotrophic bacteria), was developed to assess chemical-induced changes in aquatic heterotrophic bacterial populations in the laboratory and in natural waters. This simple, sensitive, reproducible 14 C-radiometric assay was used to monitor changes in biosynthetic activity of naturally occurring heterotrophic bacteria stimulated with an organic nutrient and incubated with known or potential aquatic chemical contaminants. Kepone at water concentrations of ≥ 1.0 mg/L significantly inhibited bacterial carboxylation; inhibition tended to follow a linear dose-response. Simazine slightly stimulated bacterial carboxylation (≥ 10 μg/L); di-2-ethylhexyl phthalate, Dylox, and mirex produced no effects (≤ 10 mg/L).

Genotoxicity testing with fish hepatic S9 for evaluation of complex mixtures in the aquatic environment: the use of channel catfish as a model

A Salmonella/fish S9 mutagenicity assay, a modification of the traditional rodent Salmonella/musome mutagenicity test of Ames, was evaluated and a working test protocol was established with channel catfish (Ictalurus punctatus) as a model system for monitoring genotoxins in complex mixtures extracted with organic solvents from freshwater sediments. Post-mitochondrial supernatant fractions (S9) from catfish mediated the biotransformation of the arylamines 2-aminoanthracene (2-AA) and 2-aminofluorene (2-AF) as well as polyaromatic hydrocarbon benzo(a)pyrene (BaP) models to Salmonella (strain TA98) mutagens, confirming other freshwater fish studies with bream, carp, pike, and rainbow trout. The enzymatic activity of catfish S9 was cytochrome P-448-450 like: inducible, heat liable, cofactor dependent, and inhibitor sensitive. Bacterial mutagenesis in the Salmonella/catfish S9 test was dose dependent and sensitive to both S9 concentrations and preincubation activation temperature. A liquid-preincubation modification of the standard plate-incorporation method significantly improved the catfish poikilothermic activation system. The hepatic S9 activity of catfish and the traditional Arochlor-1254-induced rat were qualitatively and quantitatively similar in the detection of model arylamines and benzo(a)pyrene genotoxins. The relative sensitivity of the tests, that is the lowest detectable concentration of 2-AA, 2-AF, and BaP, was <1.0 μg/plate with both activation systems. The sensitivity of the Salmonella/fish S9 assay as a screening tool to detect environmental genotoxins was clearly influenced by three test factors: preinduction of the fish, preincubation of the sample, and optimal preincubation temperature of the fish S9. The successful use of a fish activation system to mediate the biotransformation of progenotoxins establishes this Salmonella/fish S9 mutagenicity test as an ecologically relevant assay to monitor the potential aquatic hazards of environmental genotoxins influencing the aquatic resource of concern - the freshwater fisheries.