bioavailability

Cadmium (Cd) contamination in agricultural products, especially in rice, has become a global concern due to its health effects. Therefore, it is essential to develop methods for reducing cadmium accumulation in rice to maintain food safety. This article examines the effects of soil factors including redox potential, microbes, organic matter and soil pH on Cd uptake by rice plants, and presents the management practices and applicable perspectives for reducing Cd concentration in rice grains. Toxicity and Cd uptake in rice can be decreased by application of essential nutrients such as nitrogen, iron, zinc, selenium and calcium. In addition, inorganic (Lime) and organic (biochar, compost and manure) amendments have been applied in the soils to reduce Cd uptake in rice. Phytoremediation using hyperaccumulating plants can be used for the remediation of contaminated paddy soils with cadmium. Selection of low Cd accumulating rice cultivars, intercropping, crop rotation, water management and application of microbes are among the other agronomic practices successfully employed for reducing Cd concentration in rice grains. These management practices could enhance rice tolerance to Cd stress and reduce the transfer of Cd to the food chain.

The present study was carried out with the aim of determining the concentration of heavy metals (zinc, lead, cadmium, and chromium) in water, sediment, and muscle and liver tissues of Barbus sharpeyi and Barbus xanthopterus of the Karoon River in order to investigate the status of heavy metals. In this river and to determine the health of the water ecosystem of the Karoon River in Bavi City, the evaluation of these two widely consumed fish species as biological monitors of heavy metals should also be done.

This study was conducted in April 1401 in order to investigate the concentration of heavy metals such as zinc, lead, cadmium, and chromium in six stations in the Karun River in Bavi city. The statistical population for the measurement of heavy metals with three replications included 18 water samples, 18 sediment samples, and 40 benny and gotan fish. Then, in order to measure the concentration of heavy metals in water samples, the sediment and tissues of Beni and Gatan fish after acid digestion were injected into the Contra-AA 330 model atomic absorption device. A comparison of heavy metal data from water samples, sediment, and fish tissues was done using SPSS software. The Shapiro-Wilk test was also used to check the normal distribution of the results. The statistical method of one-way analysis of variance was also used for general comparisons, and Tukey's test was used for multiple comparisons, and the differences were significant at the 95% level.

The average concentration of zinc, lead, cadmium, and chromium in water samples was 5.36, 1.80, 0.18, and 0.68 micrograms/liter, respectively, in sediment samples 46.57, 13.31, 2.89, and, respectively, 22.29 μg/g. Regarding the amount of zinc, lead, cadmium, and chromium in the muscle samples of benny fish, respectively, 57.13, 1.60, 0.94, and 0.51 micrograms per gram, and 11.65, 0.91, and 56, respectively, in Gatan fish. 0.0 and 0.41 μg/g were obtained. Also, the amount of these elements in Bani fish liver is 27.33, 3.49, 2.15, and 1.51 micrograms per gram, and in Gatan fish liver it is 23.49, 2.11, 1.40, and 1.32, respectively. µg/g was obtained. Comparing the amounts of elements in the edible muscle tissue of Beni and Gatan fish showed that the amount of zinc in the muscle tissue of two species of fish is lower than the international standards, but lead, cadmium, and chromium in the muscle tissue of Beni and Gatan fish were higher than some international standards. Pearson's correlation test showed that there is a positive and significant relationship between the concentration of metals in water samples, sediment, and tissues of Bani and Gatan fish (p<0.05). The results of calculating the MPI pollution index showed that the value of this index was greater than 1 for all the investigated elements. The BAF index in all samples was less than 1, and the BCF index was greater than 1 for zinc and cadmium elements and less than 1 for lead and chromium. Also, the results of calculating the MLR index showed that the amount of this index for the studied metals is about 0.5.

The concentration of all heavy metals studied in the non-edible tissue of the liver was higher than the edible muscle tissue of Beni and Gatan fish caught from the Karun River located in Khuzestan province. The high levels of the three elements lead, cadmium, and chromium in some international standards indicate the need to pay attention to the possibility of the continuous entry of the sources of these polluting factors, such as the effluents of agricultural poisons, herbicides, insecticides, and residues from fossil fuels. The use in industrial activities depends on the habitat of the mentioned species. Based on the metal pollution index (MPI, BAF, BCF, and MLR), it can be said that among the two investigated fish species, the amount of pollution and health risk of consuming benny fish is much higher than that of gatan fish. The MPI index showed that the level of contamination in the liver is higher than in the muscle. Also, the bioaccumulation factor was higher in Bani fish than in Gatan. The bioconcentration index also shows the high accumulation power of Beni and Gatan fish for zinc and cadmium elements. Therefore, these two species are suitable biological indicators for monitoring the pollution of heavy metals such as zinc and cadmium in the Karun River. Also, considering that the highest bioconcentration index of metals is in Beni fish, Beni fish can be the most indicative species in relation to the accumulation of zinc and cadmium elements in the Karun River. The ratio of muscle to liver also showed that this index can be an important biological index in monitoring heavy metal pollution in aquatic ecosystems. The concentration of heavy metals in the liver and muscle changes with the level of environmental pollution. In polluted places, heavy metals preferentially accumulate in the liver. The results of Pearson's correlation coefficient also showed that there is a significant correlation between the concentration of metals in water and the muscle and liver tissue of Beni and Gatan fish, so it can be concluded that the muscle and liver tissue of Beni and Gatan fish can be a suitable biological monitor for Heavy metals are investigated in the Karun River, and the liver is a more suitable monitor than the muscle. In general, based on the results of this study, it can be seen that the use of fish can give a better picture of the bioavailability of heavy metals such as zinc, lead, chromium, and cadmium. Also, in terms of the health status of the Karun River, using biological monitors, the muscle tissue and liver of Bani and Gatan fish, especially the liver, can be a suitable biological monitor for river health studies. Due to the entry of agricultural, urban, etc. effluents into this area, more periodical investigations and more accurate knowledge of the concentration of pollutants in different foodstuffs such as fish, plants, and agricultural fields are necessary. Also, it is necessary to accurately identify the origin of these pollutants and their input and production sources using chemical fingerprinting techniques so that better control can be done in order to manage these pollutants and finally prevent the penetration of such pollutants into the environment. Values should be avoided.

Sediment samples were collected from 8 sites in the northern areas of Qeshm Island, Iran to determine the total and partial concentrations of heavy metals including copper (Cu), lead (Pb), nickel (Ni), cadmium (Cd), and Iron (Fe), in February 2016. A combination of nitric acid and perchloric acid was used to determine the total concentrations and sequential extraction method was used to analyze the partial concentrations of different geochemical parts of the sediment. Metal concentrations were measured by flame atomic absorption spectrometry. Contamination factor (CF), pollution load indices (PLI), enrichment factor (EF), geoaccumulation index (Igeo), risk assessment code (RAC) and potential ecological risk (PER) were calculated to determine the ecological risk. The results showed that the concentrations of heavy metals were Fe>Ni>Pb>Cu>Cd, respectively. The results of sequential extraction showed that Cd (25.98%) and Cu (21.40%) had the highest bioavailability among the other heavy metals. Most of each element was in the part of reducible (Fe-Mn oxide bound) (F3) and residual (F5). According to the RAC, only Cu and Cd were identified as high-risk at Station 5, and for other stations and other metals, the results showed low, medium or no risk. Evaluation of enrichment factor showed significant contamination for most of the metals tested, including Cd, Ni and Pb, which confirms the results from other indices. Finally, it can be said that the results of various indices that have been measured in relation to the mentioned heavy metals, showed that these elements have low to moderate pollution in the study area.