Chromium Laden Soil, Water, and Vegetables nearby Tanning Industries: Speciation and Spatial Distribution

Abstract

This study investigates the spatial distribution and speciation of chromium in water, soil, and edible plants in tannery-contaminated areas at Modjo city, Ethiopia. Modjo city is one of the industrial zones in the country, which is dominated by tanneries due to the ease of effluent discharge and water use from the nearby Modjo River crossing the city. The river, which received chromium-containing effluent from the tanneries, is also used for urban gardening of edible plants besides other domestic purposes. 12 water and 12 soil samples from contaminated areas and 6 samples from different edible plants grown nearby tanneries were collected following the standard procedure to predict the level of chromium contamination in the environment and its health risk. The total chromium in Modjo River was 20.6 mg L−1 in the upstream region which later was significantly reduced (r = –0.93, $p<0.05$ ) to 0.126 mg L−1 in the very downstream region. However, the Cr (VI) concentration ranges from 0.23 ± 0.032 to 2.82 ± 0.02 mg L−1 with a statistically insignificant decrease (r = -0.76, $p>0.05$ ) to the downstream sampling points. The lowest Cr (III) and Cr (VI) concentrations in the soil were 2.78 ± 0.37 and 4.57 ± 1.01 mg kg−1, respectively, which are higher ( $p<0.05$ ) than the control and the guideline values. Similarly, the chromium concentration in the edible plants was also 7.98 ± 0.63 mg kg−1 for green pepper to 14.45 ± 0.34 mg kg−1 for carrot with a trend of carrot > beetroot > lettuce > cabbage > tomato > green pepper. The chromium in the plants from the contaminated area was significantly higher ( $p<0.05$ ) than the control area, which is between 0.14 mg kg−1 for lettuce and 0.31 ± 0.01 mg kg−1 for tomato. It is also confirmed that the root part of plants accumulates more chromium than the leaf and the fruits. It is concluded that water and soil in tannery surroundings and edible plants grown in the area contain chromium concentrations higher than the recommended amount for a healthy environment and human consumption. Therefore, appropriate wastewater treatment, stringent regulations, and public awareness are recommended to reduce chromium contamination and its impact on public health and the environment.