The effect of heavy metals accumulation on the chlorophyll concentration of Typha latifolia plants, growing in a substrate containing sewage sludge compost and watered with metaliferus water

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Abstract

Typha latifolia plants, commonly known as cattails, were grown in a mixture of sewage sludge compost, commercial compost and perlite. Four groups (A, B, C and D) were irrigated (once every 2 weeks) with a solution containing different concentrations of Cd, Cu, Ni, Pb and Zn, where in the fifth (group M) tap water was used. At the end of the 10 weeks experimental period the mean concentration of Ni, Cu and Zn in the roots and leaves of the plants in the four groups was significantly larger to that of the plants of group M. A linear regression test satisfactorily correlated the metals’ concentrations in the irrigation solutions with the metals concentration in the leaves and roots of groups A, B, C and D. The concentration of total chlorophyll, chlorophyll a (chla) and chlorophyll b (chlb) in the leaves of the developing plants was also monitored in 2 weeks intervals. Groups A, B, C and M presented an increasing concentration of total chlorophyll, with time. In group D (stronger solution), the mean total chlorophyll concentration was reduced from 1080.69 μg/g fresh weight (f.w.) in the 8th week to 715.14 μg/g f.w., in the 10th week, a probable evidence of inhibition. When statistically tested, it was suggested that there was no significant difference between the mean chlorophyll values of the groups in each set of samples, concluding that no significant toxic action was imposed in the plants by the metals. However, when similar statistical analysis was implemented in the ratios of chla and chlb, there was significant reduction of the ratios in groups D plants, suggesting some increase in chlorophyll hydrolysis due to the metals accumulation (toxic effect) in comparison with the other groups.

Introduction

Constructed reed beds or wetlands are claimed to be low cost, low technology systems able to treat a variety of wastewaters. In Europe such systems have been successfully used for treating domestic sewage for small communities (less than 2000 people equivalent; Green and Upton, 1994, WRc and Severn Trent Water Plc, 1996, Obarska-Pempokowiak and Klimkowska, 1999). Sometimes such systems are used for the removal of heavy metals from highways runoff (Mungur et al., 1995) and acid mine drainage (Mitchel and Karathanasis, 1995). Metals are removed from wastewater by plant uptake, chemical precipitation and ion exchange and adsorption to settled clay and inorganic compounds (Gearheart, 1992, Martin and Johnson, 1995, Obarska-Pempokowiak and Klimkowska, 1999). It is likely that the potential capacity of reed beds to remove metals by plant uptake and harvesting will be small and that the ultimate removal of metals from wetland systems is probably most effectively achieved by chemical precipitation (Gearheart, 1992, Mungur et al., 1995, Mitchel and Karathanasis, 1995, Martin and Johnson, 1995, Obarska-Pempokowiak and Klimkowska, 1999).

Under that perspective an effort was made to improve the substrates performance by using materials containing large amounts of organic mater as suggested by a number of researchers (Gearheart, 1992, Mungur et al., 1995, Mitchel and Karathanasis, 1995). Sewage sludge compost was used in experiments conducted in the UK using Typha latifolia plants and artificial wastewater (Manios, 2000). The choice of sewage sludge compost as part of the substrate was based in its large composition of organic matter and the need for investigating alternative applications for sewage sludge, under the large constrains imposed in the agricultural use (EU Directive 86/278/EEC). The results indicated that the use of such material could improve substantially the ability of a substrate to retain heavy metals from wastewater (Manios, 2000).

However, the use of sewage sludge compost with large heavy metals concentration could result in an increase in the metals accumulation in the plants roots and leaves. Such a phenomenon may have an effect in the plants development and health. Heavy metals accumulation in the tissue of different plants resulted in a decrease of the biomass and the chlorophyll concentration in the leaves/stems (Burzynski and Buczek, 1989, Ouzounidou et al., 1992, Sharma and Gaur, 1995, Abdel-Basset et al., 1995).

The main aim of this research was to study the effect of heavy metals accumulation in the development of T. latifolia plants growing in sewage sludge compost containing substrate and watered with artificial wastewater, by monitoring the concentration of chlorophyll in their leaves during a short period experiment. This would allow to make a primary assumption of the combined effect in the plants’ growth and health of the heavy metals existing in both the compost and the wastewater.

Section snippets

Materials and methods

The sewage sludge compost was produced by Thames Water Plc using a windrow system with sewage sludge and straw on a 1:1 basis by volume (v/v). The chemical characteristics of the sewage sludge and the produced compost are shown in Table 1. The final material used in the pots was a mixture of this compost with commercial peat based compost 25% v/v and perlite 25% v/v. The use of peat and perlite was considered as necessary in order to avoid any phytotoxic phenomena from the compost. It is well

Results and discussion

As the experiment progressed, the amount of metals present in each pot increased in all groups, with the exemption of the blank, for which remained the same and equal to the original amount of metals existing in the substrate. Respectively, and according to Table 3, Table 4, the mean concentration of Cu, Ni and Zn in the roots and leaves of the plants, at the end of the experiment, was larger in groups A, B, C and D compared with group M. This difference was significant (5% level) according to

Conclusions

The sewage sludge compost used as a substrate component in this experiment was highly contaminated with heavy metals which however did not impose any significant effect in the development and growth of the cattails (T. latifolia) plants. There was a significant increase in the metals concentration in the plants’ tissue (roots and leaves), which was sufficiently correlated with the metals in the watering solutions and not with the metals in the substrate. There was some inhibition in the plants

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