By Ioana Papa, Sine Ross, Izabela Skowrońska and Kuan Leng Vu
Nitroaromatics are a common waste product found at the industrial sites, frequently used in various manufacturing processes. They can infiltrate into the bodies of water and contaminate them, posing a threat not only to the environment but also to human health. The specific nitroaromatics investigated in this research are 2-methyl-5-nitroaniline, 1,3-dinitrobenzene, and 2,6-dinitrotoluene and their abundance in the River Carron in relation to their distance to the industrial site of Grangemouth. The samples from sites I, II and III (see appendix 1) were processed and analyzed through gas chromatography. The results were compared to the standard chromatograms of the three investigated nitroaromatics. We show that 1,3-dinitrobenzene was present in two out of three samples, with the greatest concentration in the sample collected from the site located right in Grangemouth. To our knowledge, this was the first study investigating the impact of this particular industrial site on the pollution of the bodies of water with nitroaromatics. Further research should be conducted in this topic as we argue that the results could be impactful on the environment and health of the residents of nearby towns.
The presence of nitroaromatics in water can be an indicator of industrial contaminants from the production of materials such as dyes and pharmaceuticals(Trova et al. 1991). Grangemouth, Scotland is an industrial area based on the petrochemical industry and lies on the River Carron. The aim of this project is to determine the levels of three nitroaromatics change along the course of the river. Nitroaromatics 2-methyl-5-nitroaniline, 1,3-dinitrobenzene, and 2,6-dinitrotoluene were chosen because they are commonly used in industrial processes. This project could help determine if there are contaminants being released into the water by the industry in Grangemouth because if the level of nitroaromatics is shown to increase in the river closer to the industrial area then this could be caused by the industries in Grangemouth.
In January 2020, a 500 cm3 sample of the River Carron was collected from each of the following three sites (56° 2′ 57.7644” N, 4° 8′ 32.5464” W; 56° 0′ 39.0888” N, 3° 49′ 3.6192” W; 56° 1′ 25.86” N, 3° 43′ 38.91” W; see appendix 1). Discontinuous liquid/liquid extractions of nitroaromatics were carried out using the following procedure. Each 500 cm3 sample was shaken three times with 50 cm3 dichloromethane. The solvent was removed by a rotary evaporator. Each sample and standard solution of 1,3-dinitrobenzene, 2,6-dinitrotoluene and 2-methyl, 5-nitroaniline were analyzed by gas chromatography. The chromatograms of the samples were compared with the chromatograms of the above-mentioned nitroaromatics to deduce the presence of those nitroaromatics. If they were present in the samples, their concentrations were calculated.
The retention times for the nitroaromatic compounds that the water samples were tested for were determined using standard solutions of known concentrations.
|The concentration of the standard solution||0.0134 M||0.0109 M||0.0118 M|
Figure 1: Chromatograms of standard solutions obtained using a gas chromatograph with a sensitivity of 10-2 : (a) 2-methyl,5-nitroaniline (b) 2,6-dinitrotoluene (c)1,3-dinitrobenzene
Figure 2: Chromatograms of water samples obtained using a gas chromatograph with a sensitivity of 10-6 taken from: (a) Site I (b) Site II (c) Site III
By comparing the chromatograms of the water samples to the chromatograms of the standard solutions, we can notice that the samples taken from the site I and III contain 1,3-dinitrobenzene. It can also be concluded that the water in the Grangemouth river does not contain 2-methyl,5-nitroaniline or 2,6-dinitrotoluene.
We can calculate the concentration of the detected compound in the water samples using the surface area of the peaks.
The concentration of 1,3-dinitrobenzene at a site I can be calculated using the formula:
The concentration of 1,3-dinitrobenzene at site III was calculated using the formula:
Due to the chromatograms being obtained using two different sensitivities of the apparatus, the calculated concentrations are multiplied by an additional factor representing the ratio of the areas obtained in the case of two different chromatograms of the same solution.
Figure 3: Chromatogram of the 2-methyl,5-nitroaniline standard solution obtained using the sensitivity of the apparatus: (a) 10-2 (b) 10-6
In the collected samples, no trace of 2-methyl,5-nitroaniline and 2,6-dinitrotoluene was found. However, samples from sites I and III were found to contain 1,3-dinitrobenzene and its respective concentrations in those sites were calculated to be 3.325*10-4 M and 1.722*10-4 M. The results indicate that the close proximity to the Grangemouth industrial site correlates with an increase in the concentration of the one specific nitroaromatic as compared to the site closest to the spring of the river.
A possible reason for the water in site III containing 1,3-dinitrobenzene is that even though it was located away from the industrial site, the spot where the water was extracted is located at the start of a tourist trail with a parking lot and a restaurant/pub.
There were no traces of nitroaromatics found at site II, possibly because in site III the 1,3-dinitrobenzene already had a low concentration being located right beside the parking lot. Further down the river, the nitroaromatic could have been highly diluted and therefore impossible to detect using the method applied in this study. It was observed that the higher quality of the water in that particular spot must be known to the residents living nearby, as site II was marked as a fishing spot.
The highest concentration of 1,3-dinitrobenzene at site I fits the hypothesis as it is located in the Grangemouth industrial site, although only one out of three expected compounds was identified.
The research could be improved by analyzing samples from more sites, including a few in between the industrial site and the sea. Additionally, the research should expand by examination of the samples in search of other nitroaromatics commonly found at industrial sites, such as nitroanisoles or chloronitrobenzenes, to fully assess the scope of the problem of water contamination in such places.
Trova, C, Cossa, G, & Gandolfo, G. Behavior and fate of chloronitrobenzenes in a fluvial environment. United States. doi:10.1007/BF01700949.
Picture 1: The map showing the location of the sites the samples were taken from.