Lincoln A. Hall

The effects of dredging and reclamation on metal levels in water and sediments from an estuarine environment off Trinidad, West Indies

The levels of the metals Fe, Cr, Mn, Ni, Pb, Cu and Cd in marine sediments and sea-water were affected differently by dredging and reclamation activities carried out in a shallow coastal bay area. A two way ANOVA showed that the Mn, Ni, Pb and Cd sediment levels in the area sampled during the dredging period were significantly different (p=0.05) from the levels outside the dredging period. The levels obtained at stations along the paths of the undercurrents in the area showed similar variations to the stations close to where the currents originated for most of the metals monitored. This has been attributed to the translocation of loose dredged sediment by current action. The ANOVA also showed that the Ni and Pb sea-water levels obtained within the dredigng period were significantly different (p=0.05) from the levels obtained outside the dredging period. Marked increases in sea-water levels of Cu, Pb, and Ni occurred subsequent to dredging, apparently as a result of oxidative remobilisation of these metals in fill dumped on a reclaimed site in the vicinity. A comparison of the means of both sediment and sea-water levels within and outside the dredging period showed that the Mn sediment and Fe and Cu sea-water means were lower within the dredging period. Only Cd showed no significant difference in sediment levels between sites while CU and Cd showed no significant differences in sea-water levels between sites. Only Ni sediment levels showed a significant site-date interaction.

An evaluation of the extraction efficiencies of some common extractants for Fe, Cr, Mn, Ni, Pb and Cu on five grain-size fractionated, tropical marine sediments.

A number of extractants and extraction procedures were evaluated using a variety of tropical marine sediments fractionated on the basis of grain size. Total metal levels obtained by X-ray fluorescence analysis were used in the normalization of levels obtained by these extractants/extraction procedures. A change in extraction efficiency with change in the pH of the extractant used was observed for Fe and Mn irrespective of particle size of the fraction. Iron was extracted uniformly at each leaching level for the <53micro fractions. Manganese had comparable extraction efficiencies with both weak and strong extractants. The extraction efficiencies for Cr were generally low possibly due to an association with the residual phase. The ease with which both Pb and Ni were extracted indicated that they were only loosely bound in the sediments. The extraction efficiencies for Cu varied widely for the fractions of larger particle sizes but fell within narrow ranges for the <53micro fractions.

Complexes of squaric acid and its monosubstituted derivatives

Publisher Summary This chapter discusses complexes of squaric acid and its monosubstituted derivatives. Most of the complexes of squaric acid and its derivatives contain hydrogen bonds that have a significant influence on the tertiary structure. The prevalence of hydrogen bonding in these complexes is not surprising, because the metals in most instances have aqua ligands that hydrogen-bond either intra- or intermolecularly either to themselves or to oxygen atoms on the squarate ligands. In fact, except where steric factors prevent it, the molecules tend to maximize their hydrogen-bonding potential often resulting in distortions––sometimes large––in the coordination polyhedra of the metals. In the complexes of monosubstituted squarate ligands, the ligands, invariably utilize all the hydrogen-bonding contacts allowed by the conformational characteristics of the complex. Both intra- and intermolecular hydrogen bonding are prevalent in these complexes and this normally involves the noncoordinated ketonic oxygen atoms on the monosubstituted squarate ligands and hydrogen atoms on neighboring aqua ligands. In some instances, molecules of water of crystallization also participate in hydrogen bonding. The intermolecular hydrogen-bonding interactions in the complexes facilitate the linking of polymer chains and the formation of discrete ribbons as well as corrugated sheets.

Synthesis of ruthenium(II) monosubstituted squarates: 1. Procedural considerations ☆

Attempted syntheses of ruthenium(II) monosubstituted squarate complexes in acetonitrile using cis -[RuCl 2 (dmso) 4 ] and anisole-, methoxy-, methyl- and diphenylamino-squarate ligands, respectively, resulted in the formation in each case of the monomer cis , fac -Ru(CH 3 CN)Cl 2 (dmso) 3 ( 1 ) with the ruthenium atom in a distorted octahedral environment. A second crop of crystals harvested from the reaction with the methoxysquarate ligand was identified as the oxalato-bridged dimer [{ cis -(CH 3 CN)(Cl)(dmso) 2 Ru} 2 (μ-C 2 O 4 )] ( 2 ). When cis -[RuCl 2 (dmso) 4 ] and methylsquarate were reacted in aqueous solution instead of acetonitrile, the dimer [{ fac -(Cl)(dmso) 3 Ru} 2 (μ-C 2 O 4 )] ( 3 ) was produced. The dimers 2 and 3 are formed from oxidation/ring opening of the methoxy- and methyl-squarate ligands, respectively. Use of the salts of these ligands instead of their non-ionised forms under different reaction conditions, afforded [Na] fac -[RuCl 3 (dmso) 3 ] ( 4 ) and [(C 4 H 9 ) 4 N] 2 [(C 4 O 4 )(C 4 H 2 O 4 ) 2 ] ( 7 ), respectively, which were shown to be products of competing reactions. The information acquired from these failed attempts has provided the basis for the development of a strategy to overcome these problems and lead to a successful synthetic route to ruthenium(II) monosubstituted squarates.

Synthesis and crystal structure of a lead(II) aminosquarate

Abstract An eight-coordinate lead(II) complex, Pb(C 4 O 3 HNH 2 (OH 2 ) 2 , is produced when methanolic solutions of lead(II) nitrate and 1-amino-2-methoxycyclobutenedione are reacted. The lead shows distorted square antiprismatic coordination.

First-row transition metal complexes of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate)

Abstract Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with M(NO 3 ) 2 · x H 2 O (M=Mn, Co, Ni, Zn) in acetonitrile solutions produced a linear polymer [Mn(μ-C 6 H 5 C 4 O 3 )(C 6 H 5 C 4 O 3 )(H 2 O) 3 ] n ( 1 ) and a series of isomorphous monomeric complexes [M(C 6 H 5 C 4 O 3 ) 2 (H 2 O) 4 ] [M=Co ( 2 ), Ni ( 3 ), Zn ( 4 )]. The complex 1 contains octahedral manganese with each metal centre being bridged μ-1,3 by a phenylsquarate ligand to two neighbouring metal atoms and further coordinated to a pendant phenylsquarate ligand group and three aqua ligands. The isomorphous monomeric complexes 2 – 4 all contain two phenylsquarate ligand groups oriented trans to each other, but with the substituent phenyl group on the ligand oriented cis to the ligating oxygen atom. The coordination polyhedron in each of these monomers is completed by four aqua ligands. The polymeric manganese complex shows no significant antiferromagnetic coupling and no semiconductivity.

Synthesis and structure of cobalt(II) squarate chloride

Abstract Cobalt(II) squarate chloride [Co(HC4O4)(Cl)(C2H5OH)]2·C2H5OH has been synthesized by reacting ethanolic solutions of CoCl2·6H2O and squaric acid in a nitrogen atmosphere. Analysis of the spectroscopic data, magnetic-susceptibility and weight loss measurements suggests that the complex is five-coordinate.

Complexing properties of 1,2-dihydroxy-3,4-diketocyclobutene with iron and nickel in ethanol

Abstract The divalent chlorides of iron and nickel were reacted with 1,2-dihydroxy-3,4-diketocyclobutene (squaric acid) in ethanolic solution to form complexes of molecular formula [M(HC 4 O 4 )(Cl)(C 2 H 5 OH)] 2 ·C 2 H 5 OH in which the metal ions show penta-coordination. Both complexes are hygroscopic and on exposure to air undergo changes indicating change of coordination number. However, only the iron complex undergoes a change in oxidation state as well.

INCREASE IN HAIR LEAD, BUT NOT BLOOD LEAD CONTENT OF OCCUPATIONALLY-EXPOSED WORKERS

This study attempted to investigate whether increased hair lead concentrations due to environmental exposure are accompanied by parallel increases in blood lead concentrations. A sample set consisting of both occupationally-exposed individuals and persons from the general population was investigated. The lead content of scalp and pubic hair from the general population (n=189), traffic police personnel (n=27) and battery workers (n=22) were analysed. The hair samples were taken from the nape of the neck by cutting 23 cm closest to the scalp and cleaned using a washing procedure developed in our laboratory. The effectiveness of the washing procedure was partly determined by examining the scanning electron micrographs of the hair samples. Venous samples of blood were taken from each volunteers arm.The traffic police and battery plant operators sampled had significantly higher average scalp hair and pubic hair lead levels than the non occupationally-exposed general population. No significant differences were found between the blood lead values of these workers and the general population. Compared to the general population both occupationally-exposed groups had significantly more symptoms of lead toxicity.Lead particles were still observed on the hair shafts after the washing procedure. The amount of such lead contamination was difficult to quantify, the problem being further exacerbated by the difference in hair texture of the persons sampled. This exogenous contamination therefore detracts from the usefulness of hair as an indicator of lead exposure.

Electrochemical behaviour of polymeric complexes of monosubstituted squarate ligands. 1. Cyclic and square wave voltammetry of methylsquarate and diphenylaminosquarate complexes of cobalt and nickel

Abstract Cyclic voltammetric analysis of cobalt(II) methylsquarate in N , N -dimethylformamide (DMF) and dimethylsulphoxide (DMSO) reveals the occurrence of similar redox processes in each solvent. In DMF, one cathodic and two anodic redox processes, which are characteristic of the methylsquarate ligand, occur at −1188, +1094 and +1398 mV, respectively. Co(I)/Co(II) and Co(II)/Co(III) redox processes are also apparent. For cobalt(II) diphenylaminosquarate in DMF and DMSO, similar electrochemical processes occur but oxidation of Co(I) to Co(II) is more facile than for the methylsquarate complex in both solvents. Nickel(II) methylsquarate also shows ligand-based redox processes similar to the respective cobalt(II) complexes. Ni(I)/Ni(0) and Ni(II)/Ni(I) have been identified in the CV of this complex. In DMSO, there is evidence for partial dissociation of the nickel(II) methylsquarate complex. The results suggest that electron transfer occurs along the polymer chains in all three complexes.