Concentrations of particulate and gaseous polycyclic aromatic hydrocarbons in London air following a reduction in the lead content of petrol in the United Kingdom.

The environmental importance of tropospheric polycyclic aromatic hydrocarbons (PAH) is reviewed. The impact of reducing lead on airborne PAH is indicated and the importance of monitoring both particulate and gaseous-phase PAH is demonstrated. A Brief description of a sampling regime performed from 1985 to 1987 is given. Sampling of 18 PAH was performed and particulate lead concentrations at the kerbside were measured concurrently. Measurements indicate that there is a pronounced seasonality in PAH concentrations and in the distribution of PAH between particulate and gaseous phases. On average, 47% of the PAH measured were in the gaseous phase, indicating the importance of measuring the volatile fraction. The dominance of the common variation of each PAH was also investigated using principal components analysis. An uneven spread of data prior to and following the reduction in lead content, hindered a thorough examination of the effect of this change on PAH concentrations. However, they appeared to indicate only a small change in PAH concentration and this was linked to an increase in aromatic content of the petrol, which was much less than expected.

Effect of salinity gradients and heterotrophic microbial activity on biodegradation of nitrilotriacetic acid in laboratory simulations of the estuarine environment.

The biodegradation of nitrilotriacetic acid (NTA), a synthetic replacement detergent builder, in the estuarine environment was examined by using a laboratory estuarine simulation. Two interdependent microcosms were used; each of five vessels was equilibrated with a saline gradient between 1.30 and 17.17%, with the final vessel subsequently being increased to a maximum salinity of 31.6%. Each microcosm was seeded simultaneously with heterotrophic bacteria from both fresh and saline sources. Viable counts demonstrated the ability of each microcosm to sustain a mixed heterotrophic bacterial community throughout the range of salinities for 183 days after a stabilization period. Isolation studies demonstrated that both systems contained four bacterial species, representatives of the genera Vibrio and Flavobacterium and members of the coryneform group and the family Enterobacteriaceae. Total bacterial numbers and species diversity decreased with increased salinity. NTA was administered at low and high concentrations, one concentration to each microcosm, initially with the least amount of saline. Removal of both concentrations of NTA occurred and was attributed to biodegradation after a period of bacterial acclimatization. Subsequent dosing of NTA to vessels of higher salinity demonstrated that biodegradation was incomplete at observed mean salinities of greater than 9.18% at low influent NTA concentrations and greater than 5.08% at high influent NTA concentrations. Therefore, acclimatization was dose dependent. It was concluded that NTA acclimatization at the higher salinities ceased because of salinity stress-induced failure of NTA catabolism and not the disappearance of a particular bacterial species.

Significance and behaviour of heavy metals in wastewater treatment processes. IV. Water quality standards and criteria.

Literature on the health aspects of the presence of heavy metals in water and wastewaters is reviewed and quality standards, criteria and legislation promulgated by the World Health Organisation, European Economic Community, U.S. Environmental Protection Agency and Government of the U.S.S.R. are assessed and compared. It is evident from the literature that standards applied differ according to the projected water use and that although standards for potable water are generally based on human health criteria, other factors including available technology and economics may be limiting. Emphasis has been placed on the protection of raw water quality as a result of the limited ability of potable water treatment processes to remove certain heavy metals. It is apparent that limitations on heavy metals in discharges from the chlor-alkali and cadmium salts and pigments industries are more stringent in the United States than in the European Economic Community. It is concluded that the finite availability of unpolluted freshwater will result in greater water re-use and that appropriate standards are required to protect potable supply, raw water and agricultural land from contamination by heavy metals.