Contamination Risks And Mechanisms Of Moulds Exposure In The Urban Water Supply System Environment

The health and safety of urban water supplies has a maj or impact on the health of the population,and mould contamination can cause problems with water system maintenance and water health.There are various ways in which mould can enter a water supply system and,in addition to being carried by raw water,moulds growing in the environment are also a source of water contamination.Nutrients,moisture and temperature have been identified as important factors affecting mould growth,and other environmental factors(such as light)may also have an impact on mould growth and viability.There is currently a lack of comprehensive understanding of the presence of mycobacteria in the environment of water supply,storage and use facilities,and the risk of mycobacterial exposure and the photoresponse of mycobacteria remains to be explored.The study took the environment of typical water supply systems in urban areas,including the water-using environment,secondary water supply pumping stations and the environment of water supply and storage facilities in water plants as the objects of investigation;through sampling,plate counting and mould community diversity analysis in three ways,the occurrence and quantity of moulds in the above environment were understood,and the effects of different environmental factors(temperature,humidity and illumination)on the community structure were analysed;through the establishment of mathematical models,theoretical distribution The risk of contamination by mould spores under different environmental parameters was predicted through the establishment of mathematical models,theoretical distribution and simulation;and the influence of ambient light on the growth and viability of moulds was investigated through controlled experiments using Aspergillus(Aspergillus miscellaneous),which occurs more frequently,as the experimental object.The main findings of the study are as follows:(1)The occurrence of mould colonies in the environment of typical water supply systems in towns and cities was clarified.The highest number of colonies was detected in secondary water supply tanks and their environments(8.1 × 104 CFU/cm2),which was greater than that in residential and public water environments(3.0 × 104 CFU/cm2).The number of colonies in the water treatment plant environment decreased with the water treatment process from 7.4 × 104 to 6.7 × 104 CFU/cm2.Thermoascus spp.,Thermomyces spp.,Fusarium spp.,Mortierella spp.,Cladosporium spp.and Aspergillus spp.were found to be the core microbial groups growing in the water supply,storage and use environment.(2)The characteristics of mycobacterial communities and the factors influencing them in the environment of a typical urban water supply system were clarified.Species diversity was significantly higher(p<0.05)in both the water treatment plant and pumping station environments than in the customer(residential,public)environment.Representative genera were Thermoascus spp.in residential(LDA=5.2),Mortierella spp.in public water environments(LDA=4.5),Fusarium spp.in water supply pumping stations(LDA=4.4)and Alternaria spp.in water treatment plants(LDA=4.1).Ambient temperature and illumination were the main factors influencing the diversity and composition of the fungal communities,with Thermoascus spp.in residential dwellings showing a significant positive correlation with temperature(r=0.81,p<0.05),while Cladosporium spp.in pumping stations showed a significant negative correlation with ambient temperature(r=-0.83,p<0.05).Alternaria spp.and Aspergillus spp.in all environments were correlated with illumination at r=0.32 and r=-0.08,respectively.(3)A mathematical model of the mould spore dispersal process was developed to predict the risk of contamination from mould exposure.The model chose the Cauchy distribution as the theoretical distribution of the model,and the error between the experimental observation and the theoretical value of the model was less than 15%,which was consistent with the Cauchy distribution C(4,0)(χ2=2.01,p>0.7).According to the model predictions,the probability of spore dispersal in space decreased by 12%for each 0.1 m increase in release height and by 5%for each 0.3 m/s change in ambient air flow velocity.As wind speed increases(0-1.5m/s),the peak of the spatial dispersal probability density shifts.Spore dispersal distances increased by a factor of 3.5 when gravity was not considered,with a 37%increase in dispersal distance for each 0.1m/s increase in wind speed.In windless conditions,the effect of gravity was found to be insignificant,with the dispersal distance of mould spores ranging from 1 to 2 m.(4)The pattern of the effect of light levels on Aspergillus versicolor was explored.Light of different colour temperatures or intensities did not affect the germination of mould spores.Changes in light levels can alter colony morphology;exposure to high illumination levels resulted in slower radial growth of colonies compared to dark controls.In addition,cool light sources can have a significantly more inhibitory effect on mould growth and development than warm light sources.A noteworthy point is that earlier conidia formation of moulds in darkness or low light was not found under high illumination levels of 1050 lx,suggesting that altering ambient lighting could be used as a control strategy to mitigate mould contamination.