Purpose

Presence of heavy metals in urban agriculture is considered a major ecological risk. The aim of this research is to determine concentrations and background values of heavy metals in urban agricultural soils in Yaoundé (Cameroon), in order to assess the degree of soil pollution and to evaluate ecological risk.

Methods

Forty-five composite soil samples were taken from three market garden sites. Heavy metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). Geochemical background threshold values (GBTV) were determined using the robust statistical method of median ± median absolute deviation (MAD). Single (geoaccumulation index and enrichment factor) and complex (pollution load index and Nemerow pollution index) indices of pollution and of ecological risk (potential ecological risk index) were calculated. Significant difference between the three market garden sites was evaluated using the nonparametric test of Kruskal–Wallis.

Results

Median concentrations varied considerably, ranging from the highest to the lowest levels (mg/kg) as Mn 259.0 > Cu 111.2 > Zn 81.9 > Cr 54.6 > Pb 19.3 > Ni 14.9 > Cd 0.1. All median values were below their corresponding geochemical backgrounds, except for Pb. Single pollution indices showed that the study site was contaminated with Pb. Nemerow pollution index showed that 60% of soil samples were in the very high level of pollution. Based on potential ecological risk index, 16% of soil samples were at high risk. The three market garden sites differed significantly regarding their heavy metal contents, except Cd, as well as their pollution and ecological risk indices with the Nkolondom site having, in general, the highest levels.

Conclusions

More than half of the study area is polluted, mainly with Pb, whereas ecological risk is limited to a small part of it. This study can be used as a baseline to develop future long-term risk assessment strategies on the potential migration of heavy metals in urban agricultural soils to vegetables, animals and human beings.

中文翻译：

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喀麦隆雅温得城市农业土壤中背景值的测定以及重金属的污染和生态风险评估

目的

城市农业中重金属的存在被认为是主要的生态风险。这项研究的目的是确定雅温得（喀麦隆）城市农业土壤中重金属的浓度和背景值，以便评估土壤污染程度和评估生态风险。

方法

从三个市场花园地点采集了45个复合土壤样品。重金属（镉，铬，铜，锰，镍，铅和锌）通过电感耦合等离子体发射光谱法（ICP-OES）测定。使用中位数±中位数绝对偏差（MAD）的鲁棒统计方法确定地球化学背景阈值（GBTV）。计算了污染和生态风险的单一（地积累指数和富集因子）和复杂的（污染负荷指数和Nemerow污染指数）指数（潜在生态风险指数）。使用Kruskal–Wallis的非参数检验评估了三个市场花园地点之间的显着差异。

结果

中位数浓度变化很大，范围从最高到最低（mg / kg），如Mn 259.0> Cu 111.2> Zn 81.9> Cr 54.6> Pb 19.3> Ni 14.9> Cd 0.1。除铅外，所有中值均低于其相应的地球化学背景。单一污染指数表明研究地点被铅污染。Nemerow污染指数表明，60％的土壤样品处于很高的污染水平。根据潜在的生态风险指数，有16％的土壤样品处于高风险状态。三个市场花园用地的重金属含量（镉除外），污染和生态风险指数差异很大，其中Nkolondom用地的含量最高。

结论

研究区域的一半以上受到污染，主要是铅，而生态风险仅限于其中的一小部分。这项研究可以作为基础，用于开发有关城市农业土壤中重金属向蔬菜，动物和人类的潜在迁移的未来长期风险评估策略。