Fungal laccases degradation of endocrine disrupting compounds

Abstract

Over the past decades, water pollution by trace organic compounds (ng/L) has become one of the key environmental issues in developed countries. This is the case of the emerging contaminants called endocrine disrupting compounds (EDCs). EDCs are a new class of environmental pollutants able to mimic or antagonize the effects of endogenous hormones, and are recently drawing scientific and public attention. Their widespread presence in the environment solicits the need of their removal from the contaminated sites. One promising approach to face this challenge consists in the use of enzymatic systems able to react with these molecules. Among the possible enzymes, oxidative enzymes are attracting increasing attention because of their versatility, the possibility to produce them on large scale, and to modify their properties. In this study five different EDCs were treated with four different fungal laccases, also in the presence of both synthetic and natural mediators. Mediators significantly increased the efficiency of the enzymatic treatment, promoting the degradation of substrates recalcitrant to laccase oxidation. The laccase showing the best performances was chosen to further investigate its oxidative capabilities against micropollutant mixtures. Improvement of enzyme performances in nonylphenol degradation rate was achieved through immobilization on glass beads.

Figure 1

Chemical structure of endocrine disrupting substances used in this study.

Figure 2

Percentage degradation (%) of BPA by fungal laccases. Reaction conditions: 100 μM BPA, pH 5.0 (50 mM sodium citrate buffer), 25°C, and 1.5 U/mL laccase, with a reaction time of 1 h. All results are averages from two replicate experiments and the standard deviation is less than 10%.

Figure 3

Effect of absence of mediator, 20 μM of ABTS, or AS on the removal of EDCs after a 1 h treatment at pH 5.0 and at a temperature of 25°C with 1.5 U/mL of laccases. (a) BPA; (b) NP. All results are averages from two replicate experiments and the standard deviation is less than 10%.

Figure 4

Effect of absence of mediator, 20 μM of ABTS, or AS on the removal of EDCs mixtures by POXC. Reaction conditions: 25 μM of each molecule, pH 5.0 (50 mM sodium citrate buffer), 25°C, and 1.5 U/mL laccase, with a reaction time of 1 h. All results are averages from two replicate experiments and the standard deviation is less than 10%.

Figure 5

Percentage degradation (%) of BPA and NP by immobilized POXC. Reaction conditions: 6 U_TOT versus 25 μM each EDC, pH 5.0 (50 mM sodium citrate buffer), 25°C, and in the presence of 20 μM AS with a reaction time of 1 h. Residual laccase activity is reported as filled black circle. All results are averages from two replicate experiments and the standard deviation is less than 10%.