Christopher Mark Perkins

Biodegradation of [S,S], [R,R] and mixed stereoisomers of Ethylene Diamine Disuccinic Acid (EDDS), a transition metal chelator

An in-depth biodegradation test program was executed on the hexadentate ligand Ethylene Diamine Di Succinate (EDDS). The EDDS structure contains two chiral carbon atoms, and has three stereoisomers ([R,R], [R,S]/[S,R], [S,S]). Our research has focused on the isomer mixture (i.e. 25%[S,S]; 25%[R,R]; 50%[S,R]/[R,S], as produced from the reaction of ethylene diamine with maleic anhydride) and on the single [S,S]- and [R,R]-isomers. Biodegradation screening of the 14C-labelled EDDS isomer mixture in a Batch Activated Sludge (BAS) test with various inocula revealed incomplete mineralization, up to ca. 65% after 28 days. N-(2-aminoethyl) aspartic acid (AEAA), probably the d-isomer, was identified as the major portion of the 14C-material remaining in solution. Further testing revealed that the [S,S]-isomer is rapidly and completely mineralized in all test systems. By contrast, [R,R]-EDDS remained undegraded in a Sturm (OECD 301B) test, but was very slowly biotransformed into the recalcitrant metabolite AEAA in a BAS test. The [S,R]/[R,S] form undergoes biotransformation to AEAA in both high and low biomass systems. In a sewage treatment simulation test (OECD 303) the steady state DOC removal of mixture-EDDS in a CAS test was limited to 25-35%, even after extensive pre-acclimation, while the [S,S]-isomer achieved nearly complete removal (96%). This study illustrates the importance stereospecificity may have on the biodegradation and metabolite formation of a chemical. A biodegradation scheme for the different EDDS stereoisomers is proposed.

The structure of cobalt methylmalonate complexes, CoClN4O7C10H28 and CoCl2N4O5.5C11H28, models for metal complexes of γ-carboxyglutamic acid

Abstract Methylmalonato-2,2′,2″-triaminotriethylaminecobalt(III) chloride was synthesized by two methods, the first involving the addition of 2,2′,2″-triaminotri- ethylamine (tren) to a basic solution of cobalt(II) methylmalonate prepared from methylmalonic acid and cobalt(II) chloride and the second involving the addition of disodium methylmalonate to a solution of [Co(tren)C12] C1·H2O. Crystals of the complex are monoclinic, space group P21/c, a=8.438(2), b = 22.770(7), c = 9.913(3) A, β = 114.6(1)°, Z = 4. The asymmetric unit consists of one complex, a chloride counter ion and three water molecules. A protonated complex was generated in an acidic solution of the first compound and was also characterized crystallographically. The crystals are again monoclinic, space group P21/n, a=9.112(3), b=16.587(4), c= 12.610(4) A, β = 99.32(2)°, Z = 4. In this case, the asymmetric unit contains the complex, two chloride ions, a water molecule and half of an ethanol molecule. A strong hydrogen bond involving one of the carboxylate oxygens not bound to the metal allows the methylmalonate ion to serve as a uninegative, bidentate ligand. This mode of binding suggests a model for how proteins with two adjacent γ-carboxyglutamic acid residues might bind one Ca2+ without causing severe charge balance problems.

Metal levels in whales from the Gulf of Maine: A One Environmental Health approach

One Environmental Health has emerged as an important area of research that considers the interconnectedness of human, animal and ecosystem health with a focus on toxicology. The great whales in the Gulf of Maine are important species for ecosystem health, for the economies of the Eastern seaboard of the United States, and as sentinels for human health. The Gulf of Maine is an area with heavy coastal development, industry, and marine traffic, all of which contribute chronic exposures to environmental chemicals that can bioaccumulate in tissues and may gradually diminish an individual whales or a populations fitness. We biopsied whales for three seasons (2010-2012) and measured the levels of 25 metals and selenium in skin biopsies collected from three species: humpback whales (Megaptera novaeangliae), fin whales (Balaenoptera physalus), and a minke whale (Balaenoptera acutorostrata). We established baseline levels for humpback and fin whales. Comparisons with similar species from other regions indicate humpback whales have elevated levels of aluminum, chromium, iron, magnesium, nickel and zinc. Contextualizing the data with a One Environmental Health approach finds these levels to be of potential concern for whale health. While much remains to understand what threats these metal levels may pose to the fitness and survival of these whale populations, these data serve as a useful and pertinent start to understanding the threat of pollution.