Soil Macrofauna and its Relationship with Trace Metals under Different Cacao Cultivation Management Systems in the Central Rainforest Region of Peru

Cruz-Cerrón, Dana; Alvarez-Tolentino, Daniel; Reategui-Inga, Manuel; Paccosonco-Sucapuca, Leonel; Cabrera-Montalvo, Abrahams; Susanibar-Sandoval, Daniel; Alvarez-Orellana, Julio

doi:10.21577/0103-5053.20260104

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Full Paper • J. Braz. Chem. Soc. 37 • 2026 • https://doi.org/10.21577/0103-5053.20260104 linkcopy

Soil Macrofauna and its Relationship with Trace Metals under Different Cacao Cultivation Management Systems in the Central Rainforest Region of Peru

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Few studies in the Peruvian Amazon have jointly evaluated soil macrofauna and heavy metal contamination in cacao agroecosystems. This study integrated ICP-MS (inductively coupled plasma mass spectrometer) multielement analysis, soil macrofauna assessment, and multivariate statistics in five cacao plots (113-1,102 m above sea level) under monoculture and diversified management with varying fertilization and pesticide inputs. Twelve elements were quantified in 25 composite soil samples, and macrofauna were collected from 25 soil monoliths (25 cm × 25 cm × 20 cm), yielding eight taxa. As, Cd, and Pb ranged from 1.74-8.42, 0.139-0.964, and 8.21-53.9 ppm, respectively, with peak concentrations in plot P05. Plot P02, under diversified management, showed the greatest macrofaunal diversity (S = 4.6 (species richness); H = 1.15 (Shannon diversity index). Hymenoptera (1,060 individuals) and Oligochaeta (257 individuals) dominated the community, while Coleoptera, Isopoda, and Blattodea were scarce. Most metal-macrofauna correlations were weak; however, significant positive associations were detected between sulfur and Helicidae (ρ = 0.401 (Spearman rank correlation coefficient), p < 0.05) and chromium and Coleoptera (ρ = 0.465, p < 0.05). These findings suggest that soil mineral composition and management practices, beyond toxic-metal loads alone, jointly shape macrofaunal structure, underscoring the need for sustainable soil monitoring in the Central Rainforest Region of Peru.

Keywords:
ICP-MS; soil biodiversity; cacao management; tropical agroecosystems; trace elements; Chanchamayo

Sampling plot	UTM coordinate		Altitudea / m	Plot description
Sampling plot	North	East	Altitudea / m	Plot description
P1	8,768,329.327	461,270.17	847	monoculture management, fertilization based on mulch
P2	8,767,392.49	460,289.97	882	diversified management, fertilization based on urea and mulch
P3	8,767,420.15	460,841.55	1102	monoculture management, fertilization based on urea and mulch
P4	8,766,648.406	460,149.14	963	diversified management, fertilization with a smaller amount of leaf litter (mulch), guinea pig manure, and cacao residues; use of pesticides
P5	8,767,311.041	460,166.46	887	diversified management, fertilization based on urea, seabird guano, and mulch

Element	LOD / ppm	LOQ / ppm	CRM Buffalo River Sediment (NIST 2704)
Element	LOD / ppm	LOQ / ppm	Certified value / ppm	Determined value / ppm	Recovery / %
Cd	0.002	0.007	3.45 ± 0.22	3.39 ± 0.01	98.2
Pb	0.002	0.006	161 ± 17	179.3 ± 0.1	111.4
As	0.011	0.037	23.4 ± 0.8	16.22 ± 0.01	69.3
Cr	0.013	0.043	135 ± 5	93.52 ± 0.02	69.2
Mn	0.005	0.018	544 ± 21	480.3 ± 0.2	88.3
Fe	0.119	0.396	41100 ± 1000	33125 ± 15.5	80.6
Cu	0.009	0.031	98.6 ± 5.0	81.69 ± 0.05	82.8
Mg	0.309	1.029	12000 ± 200	6052 ± 3.4	50.4ª
Al	0.235	0.782	61100 ± 1600	10833 ± 7.3	17.7ª
P	0.594	1.979	997 ± 42	590.3 ± 0.3	59.2
S	3.711	12.37	3970 ± 110	4846 ± 2.0	122.1
K	1.287	4.282	20000 ± 400	1766 ± 2.1	8.8ª

Element	P1 / ppm (n = 5)	P1 / ppm (n = 5)	P1 / ppm (n = 5)	P1 / ppm (n = 5)	P1 / ppm (n = 5)	p-value
Cd	0.258 ± 0.0812^c	0.532 ± 0.173^ab	0.406 ± 0.182^abc	0.331 ± 0.140^bc	0.752 ± 0.231ª	0.007
Pb	14.9 ± 4.07^bc	22.4 ± 6.5^ab	21.6 ± 9.73^ab	13.0 ± 2.93^c	42.6 ± 11.0a	0.003
Mg	1900 ± 660^a	2750 ± 651^a	3040 ± 582^a	3770 ± 1890ª	2820 ± 1120ª	0.225
Al	10400 ± 2390^a	10400 ± 2130^a	10500 ± 2590^a	11900 ± 4780ª	15400 ± 2670^a	0.174
P	931 ± 723^a	597 ± 261^a	589 ± 291^a	499 ± 114ª	673 ± 188^a	0.831
S	2500 ± 84^a	2610 ± 126^a	2470 ± 62.5^a	2540 ± 82.0^a	2590 ± 56.2^a	0.111
K	1240 ± 103^b	1720 ± 308^ab	1670 ± 525^ab	2220 ± 1140^ab	2390 ± 762^a	0.049
Cr	15.2 ± 3.93^a	13.0 ± 2.57^a	19.8 ± 5.66^a	14.6 ± 3.59ª	18.5 ± 2.86^a	0.054
Mn	442 ± 40.3^b	557 ± 191^ab	560 ± 161^ab	493 ± 86.8^ab	771 ± 92.5^a	0.036
Fe	12800 ± 967^b	14900 ± 2540^ab	16400 ± 2860a^b	17100 ± 5430^ab	19600 ± 2800^a	0.049
Cu	11.4 ± 2.39^a	14.1 ± 3.10^a	12.3 ± 4.00^a	11.0 ± 2.21ª	16.2 ± 2.90^a	0.156
As	3.59 ± 1.43^cd	5.10 ± 1.30^bc	6.09 ± 1.28^ab	2.95 ± 0.696^d	7.72 ± 0.820^a	0.001
Different letters (a, b, c, d) in the same row indicate significant differences at a 95% confidence level according to Tukey’s test (p < 0.05); P1 to P5 represent different cacao cultivation management plots; n: number of samples; p-value: probability value.

Taxonomic composition			Plot					Total number of individuals
Class	Order	Family	P1	P2	P3	P4	P5	Total number of individuals
Clitellata	Opisthopora	Lumbricidae	84	26	55	29	63	257
Diplopoda	Symphyla	Scolopendrellidae	30	44	6	8	4	92
Insecta	Hymenoptera	indeterminado	239	168	186	35	432	1060
	Coleoptera	indeterminado	5	0	12	13	8	38
	Blattodea	Blaberidae	0	0	0	0	2	2
Arachnida	Aranea	Aranea	5	15	7	121	0	148
Malacostraca	Isopoda	indeterminado	0	44	11	5	4	64
Gastropoda	Stylommatophora	Heicidae	0	9	0	0	1	10

Plot	Species richness index (S)	Abundance	Shannon diversity index (H)	Simpson evenness index (E)	Simpsons dominance index (D)
P1	2.8	72.60	0.60	0.33	0.67
P2	4.6	61.20	1.15	0.59	0.41
P3	4.4	55.40	1.03	0.55	0.45
P4	3.6	42.20	0.87	0.48	0.52
P5	4.2	102.80	0.58	0.29	0.71

Metal	Spearman correlation coefficient (ρ)
Metal	Oligochaeta	Myriapoda	Hymenoptera	Araneae	Coleoptero	Isopoda	Helicidae	Blaberidae
Cd	-0.221	-0.067	0.052	-0.049	0.061	0.194	0.329	0.283
Pb	-0.133	-0.186	0.096	-0.157	0.247	0.1	0.292	0.226
Mg	-0.323	-0.101	-0.183	0.038	0.028	0.026	0.159	0.057
Al	-0.112	-0.229	-0.043	-0.323	0.213	-0.124	0.157	0.198
P	-0.115	-0.019	-0.3	-0.286	-0.127	-0.116	0.133	0.198
S	-0.157	0.13	-0.119	0.007	-0.32	0.079	0.40a	0.17
K	-0.32	-0.193	0.007	-0.117	0.187	0.098	0.188	0.198
Cr	0.14	-0.332	-0.044	-0.335	0.465^{^*}	-0.138	-0.022	0.311
Mn	-0.148	-0.272	-0.063	-0.002	0.285	0.048	0.319	0.311
Fe	-0.141	-0.323	-0.12	-0.097	0.351	0.005	0.19	0.226
Cu	-0.153	-0.099	-0.066	-0.123	-0.033	0.084	0.28	0.226
As	-0.076	-0.102	0.184	-0.252	0.292	0.049	0.344	0.142

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[1] Fieldwork was carried out at the end of July and during August 2023, in the winter season, when rainfall was scarce.

[TFN1] ^a
Above sea level; UTM: Universal Transverse Mercator.