Toxicity thresholds (ECx) for Cr in soils and prediction models

doi:10.13745/j.esf.sf.2023.11.55

Abstract

Abstract:

The lack of toxicology data is the main factor hindering the ecological risk assessment of Cr contamination in soils and the revision of soil environmental quality standards in China. In this study, we conduct toxicology tests on seven soil types (with different soil properties) in China, using earthworm biomass, cabbage biomass, and microbial matrix induced respiration (SIR) as measurement endpoints. We determined the effective concentration (EC_x) values under different soil types based on the Log-logistic dose-effect relationship and low-dose stimulus effect function model. On this basis we developed predictive models for estimating toxicity thresholds of Cr under different soil properties. Chromium toxicity in earthworms, Chinese cabbage, and soil microorganisms under different soil types showed significant inhibitory effect with increased soil Cr concentrations, and the dose-response (D-R) relationship was clearly sigmoid in shape. Under different soil types, the EC₁₀ values for soil microorganisms (SIR), earthworms, and Chinese cabbage ranged between 22.1-53.7, 65.0-137.2, and 82.1-220.2 mg/kg, respectively, and the EC₅₀ values between 50.3-103.7, 103.9-369.0, and 159.9-441.9 mg/kg, respectively. The Cr toxicity thresholds for the tested species, from high to low, followed the order of Chinese cabbage>earthworms>soil microorganisms, with soil microorganisms being the most sensitive to Cr toxicity. Under low Cr concentrations (<112 mg/kg), the tested species showed significant hormesis effects, among which earthworms had a maximum hormesis between 102%-108% under different soil types, and Chinese cabbage between 105%-112%, while soil microorganisms showed relatively small effect at 104%. Chromium toxicity thresholds under different soil types can be well predicted based on soil pH and clay/CEC contents. The research results provide a scientific basis for the ecological risk assessment of Cr in soils and for the formulation and revision of environmental quality standards for Cr in soils.

Key words: chromium, dose-response, hormesis, toxicity threshold

CLC Number:

SUN Xiaoyi, WANG Meng, QIN Luyao, YU Lei, WANG Jing, CHEN Shibao. Toxicity thresholds (EC_x) for Cr in soils and prediction models[J]. Earth Science Frontiers, 2024, 31(2): 121-129.

Figures/Tables 6

Table 1 Soil properties of the seven soil types tested

土壤地点		土壤类型	pH	土壤CEC/ (cmol·kg^-1)	OC含量/%	黏土含量/%	总Cr含量/ (mg·kg^-1)
海口(HK)	20°02'45.97″N, 110°11'38.39″E	砖红壤	4.93	8.75	1.51	23.00	48.21
桂林(GL)	25°27'35.66″N, 110°29'01.94″E	红壤	5.75	18.65	3.24	27.80	74.52
衡阳(HY)	26°89'32.31″N, 112°57'19.97″E	红壤	6.64	16.59	2.82	28.20	77.94
嘉兴(JX)	30°74'61.29″N, 120°75'54.86″E	水稻土	6.72	20.65	3.46	38.90	75.53
新乡(XX)	35°18'13.71″N, 113°55'15.05″E	潮土	7.30	12.82	1.05	15.80	61.38
保定(BD)	38°87'38.91″N, 115°46'48.15″E	潮土	8.15	9.52	1.21	20.63	54.59
德州(DZ)	37°16'53.14″N, 116°43'40.56″E	潮土	8.90	8.33	0.69	12.00	49.46

Fig.1 The dose-response curves of Cr based on various test endpoints in soils

Table 2 Effective concentration (ECx, mg/kg) values of Cr under different soil types

土壤地点	蚯蚓
土壤地点	EC₁₀/(mg·kg^-1)	EC₅₀/(mg·kg^-1)	EC₁₀/(mg·kg^-1)	EC₅₀/(mg·kg^-1)	EC₁₀/(mg·kg^-1)	EC₅₀/(mg·kg^-1)
HK	65.0	103.9	82.1	159.9	22.1	50.3
	(39.2~71.5)	(88.5~119.5)	(50.1~96.3)	(149.2~171.3)	(11.8~34.8)	(38.0~62.7)
GL	85.9	187.9	126.6	261.2	42.0	74.9
	(52.8~133.9)	(168.1~209.9)	(72.0~195.5)	(216.1~315.6)	(20.3~68.3)	(60.2~102.4)
HY	109.2	171.5	133.3	294.3	47.0	83.0
	(78.0~152.8)	(150.6~207.4)	(79.0~199.9)	(245.8~352.5)	(22.0~79.1)	(63.5~127.1)
JX	107.1	259.3	173.8	321.8	53.7	92.4
	(70.5~187.1)	(225.4~298.3)	(95.8~223.5)	(270.9~382.3)	(36.9~78.1)	(72.3~117.0)
XX	85.1	253.3	105.0	302.4	36.0	81.2
	(48.0~124.6)	(159.7~281.2)	(67.0~143.3)	(175.5~333.4)	(25.0~51.8)	(67.8~97.2)
BD	137.2	369.0	220.2	441.9	42.7	103.7
	(65.8~193.5)	(345.8~496.0)	(81.4~277.4)	(203.7~487.3)	(25.3~72.1)	(65.5~122.8)
DZ	122.4	267.8	189.0	367.9	37.1	79.9
	(60.7~196.0)	(198.2~338.3)	(64.0~223.8)	(143.7~396.1)	(21.5~64.3)	(54.2~96.3)

Fig.2 Comparison of EC10 and EC50 values of Cr between different species under different soil types

Table 3 Chromium(VI)-induced hormesis in different species under different soil types

土壤地点	蚯蚓			小白菜				SIR
土壤地点	Cr^*含量/(mg·kg^-1)	效应/%		Cr含量/(mg·kg^-1)		效应/%		Cr含量/(mg·kg^-1)		效应/%
HK
GL	102.4	104	105.2		105
HY	98.1	103	102.8		108		89.4		102
JX	98.7	108	99.6		112		87.6		104
XX			96.8		105
BD	106.3	102	95.9		106
DZ

Table 4 Linear regression relationship between ECx values (Cr) and soil properties based on different toxicity endpoints

物种	回归方程	R²
蚯蚓	lgEC₁₀=0.924+0.358 lgpH+0.671 lgCEC	0.761^*
	lgE $C 1 0$ =1.013+0.717 lgpH+0.253 lgCEC+0.322 lg [w(OC)/%]	0.849^**
	lgEC₅₀=1.037+0.439 lgpH+0.747 lg [w(OC)/%]	0.702^*
	lgEC₅₀=1.161-0.934 lgpH+0.170 lgCEC+0.444 lg [w(OC)/%]	0.832^*
	lgEC₅₀=0.561+0.845 lgpH+0.342 lgCEC+0.086 lg [w(OC)/%]+0.420 lg [w(Clay)/%]	0.864^**
小白菜	lgE $C 1 0$ =1.132+0.357 lgpH+0.564 lgCEC	0.655^*
	lgE $C 1 0$ =1.235+0.767 lgpH+0.087 lgCEC+0.368 lg [w(OC)/%]	0.799^*
	lgEC₁₀=1.023+0.833 lgpH+0.833 lg [w(Clay)/%]+0.197 lg [w(OC)/%]	0.815^*
	lgEC₅₀=1.333+0.341 lgpH+0.670 lgCEC	0.615^*
	lgEC₅₀=1.474+0.905 lgpH+0.013 lgCEC+0.506 lg [w(OC)/%]	0.795^*
SIR	lgEC₁₀=0.489+1.120 lgpH+0.572 lg [w(OC)/%]	0.750^*
	lgE $C 1 0$ =-0.045+0.683 lgpH+0.694 lgCEC+0.010 lg [w(OC)/%]+0.191 lg [w(Clay)/%]	0.860^*
	lgEC₅₀=0.926+1.021 lgpH+0.533 lg [w(OC)/%]	0.726^*
	lgEC₅₀=0.461+0.579 lgpH+0.692 lgCEC+0.141 lg [w(Clay)/%]	0.853^**
	lgEC₅₀=0.668+0.628 lgpH+0.611 lgCEC+0.138 lg [w(OC)/%]	0.852^**

Table 4 Linear regression relationship between ECx values (Cr) and soil properties based on different toxicity endpoints

物种	回归方程	R²
蚯蚓	lgEC₁₀=0.924+0.358 lgpH+0.671 lgCEC	0.761^*
	lgE $C 1 0$ =1.013+0.717 lgpH+0.253 lgCEC+0.322 lg [w(OC)/%]	0.849^**
	lgEC₅₀=1.037+0.439 lgpH+0.747 lg [w(OC)/%]	0.702^*
	lgEC₅₀=1.161-0.934 lgpH+0.170 lgCEC+0.444 lg [w(OC)/%]	0.832^*
	lgEC₅₀=0.561+0.845 lgpH+0.342 lgCEC+0.086 lg [w(OC)/%]+0.420 lg [w(Clay)/%]	0.864^**
小白菜	lgE $C 1 0$ =1.132+0.357 lgpH+0.564 lgCEC	0.655^*
	lgE $C 1 0$ =1.235+0.767 lgpH+0.087 lgCEC+0.368 lg [w(OC)/%]	0.799^*
	lgEC₁₀=1.023+0.833 lgpH+0.833 lg [w(Clay)/%]+0.197 lg [w(OC)/%]	0.815^*
	lgEC₅₀=1.333+0.341 lgpH+0.670 lgCEC	0.615^*
	lgEC₅₀=1.474+0.905 lgpH+0.013 lgCEC+0.506 lg [w(OC)/%]	0.795^*
SIR	lgEC₁₀=0.489+1.120 lgpH+0.572 lg [w(OC)/%]	0.750^*
	lgE $C 1 0$ =-0.045+0.683 lgpH+0.694 lgCEC+0.010 lg [w(OC)/%]+0.191 lg [w(Clay)/%]	0.860^*
	lgEC₅₀=0.926+1.021 lgpH+0.533 lg [w(OC)/%]	0.726^*
	lgEC₅₀=0.461+0.579 lgpH+0.692 lgCEC+0.141 lg [w(Clay)/%]	0.853^**
	lgEC₅₀=0.668+0.628 lgpH+0.611 lgCEC+0.138 lg [w(OC)/%]	0.852^**

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